• 沒有找到結果。

Effects of annealing temperature on microstructural development at the interface between zirconia and titanium

N/A
N/A
Protected

Academic year: 2021

Share "Effects of annealing temperature on microstructural development at the interface between zirconia and titanium"

Copied!
7
0
0

加載中.... (立即查看全文)

全文

(1)

Effects of Annealing Temperature on Microstructural Development at

the Interface Between Zirconia and Titanium

Kun-Lin Lin and Chien-Cheng Lin*

,w

Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu 30050, Taiwan The interfacial reaction layers in the Ti/ZrO2diffusion couples,

isothermally annealed in argon at temperatures ranging from 11001 to 15501C for 6 h, were characterized using scanning electron microscopy and transmission electron microscopy, both attached with an energy-dispersive spectrometer. Very limited reaction occurred between Ti and ZrO2at 11001C. Ab0-Ti(Zr, O) layer and a two-phase a-Ti(O)1b0-Ti(Zr, O) layer were found in the titanium side after annealing at T 13001C and T 14001C, respectively. A three-phase layer, consisting of Ti2ZrO1a-Ti(O, Zr)1b0-Ti (O, Zr), was formed after anneal-ing at 15501C. In the zirconia side near the original interface, b0-Ti coexisted with fine spherical c-ZrO2x, which dissolved a significant amount of Y2O3 in solid solution at T 13001C. Further into the ceramic side, thea-Zr was formed due to the exsolution of Zr out of the metastable ZrO2xafter annealing at T 13001C: the a-Zr was very fine and dense at 13001C, continuously distributed along grain boundaries at 14001C, and became coarsened at 15501C. Zirconia grains grew significantly at T 14001C, with the lenticular t-ZrO2xbeing precipitated in c-ZrO2x. Finally, the microstructural development and diffusion paths in the Ti/ZrO2 diffusion couples annealed at various temperatures were also described with the aid of the Ti–Zr–O ternary phase diagram.

I. Introduction

T

HEinterfacial reactions between titanium and zirconia have been studied in the past several decades.1–3It is generally accepted that the oxygen of zirconia is readily dissolved into the titanium to form a-Ti(O), resulting in the blackening of oxygen-deficient zirconia (ZrO2x). Various reaction layers in the

inter-face between titanium and zirconia were found.4,5 However, they were not fully explored because of the limitations of the analytical instruments. Meanwhile, some researchers6,7

indi-cated that the titanium additive could improve the mechanical properties of zirconia including strength and thermal shock re-sistance.

Recently, Lin and colleagues8–13have thoroughly investigated the diffusional reactions between titanium (or titanium alloys) and zirconia. Using transmission electron microscopy (TEM)/ energy-dispersive spectrometer (EDS) analyses, they indicated that the ordered titanium suboxide (Ti3O) and the orthorhombic

lamellae Ti2ZrO were formed in the solid solution of a-Ti(O)

between zirconia and titanium melt during cooling from 17001C.9 In addition, the orthorhombic b0-Ti(Zr, O) and a spherical-ordered Ti2ZrO phase were also found in the metal

side of the Ti/ZrO2diffusion couple after annealing at 15501C.11

The orientation relations between a-Ti(Zr, O) and lamellae

Ti2ZrO were determined to be ½0001aTi==½110Ti2ZrO and ð1010ÞaTi==ð110ÞTi2ZrO; meanwhile, those between a-Ti(O) and spherical-ordered Ti2ZrO were½0001aTi==½0001Ti2ZrOand ð1010ÞaTi==ð1010ÞTi2ZrO.11 Furthermore, the acicular a-Ti(O)

was precipitated in the b0-Ti(O, Zr) matrix with two various orientation relations in the metal side.13 One was determined to be½2110aTi//[001]b0-Tiand (0001)a-Ti//(100)b0-Tiand the other ½2110aTi//[021]b0-Ti and (0001)a-Ti//ð112Þb0-Ti.13 In the zirconia side, far away from the interface of Ti/ZrO2, Lin and Lin12

also observed twinned t0-ZrO

2x, lenticular t-ZrO2x, and/or

ordered c-ZrO2xas well as the intergranular a-Zr after

anneal-ing at 15501C.

Even though extensive studies were carried out on the inter-face reactions between titanium and zirconia, the temperature effects on the microstructure evolution have not been well known to date. In order to shed light on the temperature effects on the microstructural evolution of the various distinct reaction layers between titanium and zirconia, the Ti/ZrO2

diffusion couples were isothermally annealed in argon at 11001, 13001, 14001, and 15501C, respectively, for 6 h in the present study. Various microstructures were characterized using scanning electron microscopy (SEM) and TEM, both attached with an EDS. Through the comparison among various micro-structures, an attempt was made to propose the microstructural development of the reaction layers between titanium and zirco-nia at various annealing temperatures, while diffusion paths were depicted in the Ti–Zr–O ternary phase diagram.

II. Experimental Procedures (1) Sample Preparation

Bulk ZrO2specimens were prepared from the powder of 3 mol%

Y2O3partially stabilized zirconia by the hot press (Model

HP50-MTG-7010, Thermal Technology Inc., Santa Rosa, CA). The nominal composition of the zirconia powder was supplied by the vendor (Toyo Soda Mfg. Co., Tokyo, Japan) as follows: 494 wt% ZrO21HfO2 (accounting for approximately 2%–3% of

this total), 5.4 wt% Y2O3, o0.001 wt% Fe2O3,o0.01 wt%

SiO2,o0.005 wt% Na2O,o0.005 wt% TiO2,o0.02 wt% Cl,

and o0.005 wt% SO42. Both as-hot-pressed ZrO2specimens

and commercially available titanium billets (with a nominal composition of 99.31 wt% Ti, 0.25 wt% O, 0.01 wt% H, 0.03 wt% N, 0.10 wt% C, 0.30 wt% Fe; Kobe Steel Ltd., Tokyo, Japan) were cut and machined to the dimensions of 14 mm 14 mm 5 mm. One Ti billet was inserted in between two ZrO2

specimens to form a sandwiched sample, which was then slightly pressed and annealed at 11001, 13001, 14001, and 15501C, re-spectively, for 6 h in an atmospheric argon. The hot-pressing procedures of both bulk ZrO2and the sandwiched samples have

been described in detail elsewhere.11

(2) SEM/EDS Analyses

A SEM (Model JSM-6330F, JEOL Ltd., Tokyo, Japan) equipped with an EDS (Mode ISIS300, Oxford Instrument Inc., London, U.K.) was used for the microstructural observa-tion on the interface between titanium and zirconia. Both T. E. Mitchell—contributing editor

Supported by the National Science Council of Taiwan under Contract No. NSC 93-2216-E-009-017.

*Member, American Ceramic Society. w

Author to whom correspondence should be addressed e-mail: chienlin@ faculty.nctu.edu.tw

Manuscript No. 21546. Received March 3, 2006; approved August 2, 2006.

Journal

DOI: 10.1111/j.1551-2916.2006.01352.x r2007 The American Ceramic Society

(2)

backscattering electron image (BEI) and secondary electron im-age (SEI) were acquired. Cross-sectional specimens were cut into about 3 mm 2 mm  1 mm, and then ground and polished using a diamond paste down to 1 mm. The specimens for the SEI observation were etched by the Kroll reagent (10 mL HF130 mL HNO3160 mL H2O) for 15 s. In order to avoid electric

charging under the electron beam, specimens were coated with a thin layer of platinum.

(3) TEM/EDS Analyses

A TEM (Model JEM 2000Fx, JEOL Ltd.) equipped with an EDS (Mode ISIS300, Oxford Instrument Inc.) was also used for characterizing the interfacial microstructure between titanium and zirconia. Cross-sectional TEM specimens perpendicular to the interface of titanium and zirconia were cut, ground, and polished by standard procedures as mentioned previously.11The TEM specimens were dimpled and ion milled by a precision ion miller (Model 691, Gatan Inc., Pleasanton, CA). The quantita-tive composition analyses were carried out based on the prin-ciple of the Cliff–Lorimer standardless technique.14

III. Results and Discussion

(1) Distinct Microstructures at Various Temperatures The microstructure of the Ti/ZrO2interface strongly depended

on the annealing temperature. Figures 1(a)–(d) display the BEIs of the cross section normal to the Ti/ZrO2 interface after

an-nealing at 11001, 13001, 14001, and 15501C for 6 h, respectively. Titanium was in the left-hand side, while zirconia was on the other side. The vertical arrows in the upper side of individual figures indicate the original interfaces of Ti and ZrO2. The

ori-ginal interfaces were deliberately located by the results of char-acteristic KaX-ray maps of yttrium (not shown), which were

relatively immobile compared with elements Zr, O, and Ti. (A) Reaction Layer ‘‘I’’ of the Ti/ZrO2 Interface: A gray thin layer (designated as the reaction layer ‘‘I’’) was formed in the interface between Ti and ZrO2 at temperatures

T 14001C as shown in Figs. 1(c) and (d). The reaction layers ‘‘I’’ in Figs. 1(a) and (b) were invisible because of the limited resolution; however, they could be observed using SEM or TEM at a higher magnification [Figs. 2(a) and 3]. To the left of the reaction layer ‘‘I’’ was the a-Ti with oxygen in solid solution, designated as a-Ti(O) in this study.

Figure 2 displays the SEIs of the lamellar a-Ti (Zr, O) and Ti2ZrO in the reaction layer ‘‘I’’ etched by Kroll reagent (10 mL

HF130 mL HNO3160 mL H2O) after annealing at 13001,

14001, and 15501C, respectively. The thickness of the reaction layer ‘‘I’’ increased with temperature. Figure 2 shows clearly, at a higher magnification, the very different microstructures devel-oped at various anneal temperatures. For example, the sequence of the reaction layers I1IV1y [Fig. 2(a)] was formed after an-nealing at 13001C, while the sequence of the reaction layers I1III1y [Fig. 2(b)] and the sequence of the reaction layers I1II1y [Fig. 2(c)] were formed after annealing at 14001 and 15501C, respectively.

For the benefit of good resolution of TEM, a very thin reac-tion layer ‘‘I’’ was found in the Ti/ZrO2interface after annealing

at 11001C for 6 h. Figure 3(a) displays the TEM micrograph of the cross section between Ti and ZrO2after annealing at 11001C

for 6 h. The arrow indicates the original interface, with titanium and zirconia being in the upper and lower sides, respectively. Their morphologies were very different from results in previous studies after annealing at 15501 or 17001C.9,11The SADPs as shown in Fig. 3(b) indicated that the lamellar phases were composed of orthorhombic Ti2ZrO and hexagonal disordered

a-Ti(Zr, O). The orientation relationship of Ti2ZrO and a-Ti(Zr,

O) could be expressed as follows: ½0001a-Ti//½110Ti2ZrO and ð1010ÞaTi==ð110ÞTi2ZrO. The EDS, shown in Fig. 3(c), indicated that the Ti2ZrO consisted of 56.1 at.% Ti, 22.9 at.% Zr, and

21.0 at.% O.

(B) Reaction Layer ‘‘II’’ of the Ti/ZrO2 Interface: The lamellar a-Ti(Zr, O) and Ti2ZrO along with b0-Ti(Zr, O)

(desig-nated as the reaction layer ‘‘II’’), as indicated previously,11were observed in the Ti/ZrO2interface after annealing at 15501C/6 h

[Fig. 1(d)]. In contrast, no such lamellar structure was found in the samples after annealing between 11001 and 14001C.

(C) Reaction Layer ‘‘III’’ of the Ti/ZrO2Interface: The two-phase acicular a-Ti(Zr, O)1b0-Ti(Zr, O) layers (designated as the reaction layer ‘‘III’’) after annealing at 14001 and 15501C are shown in Figs. 1(c) and (d), respectively. The reaction layer ‘‘III’’ appeared as a relatively minor layer at 15501C compared with the reaction layer ‘‘II,’’ as shown in Fig. 1(d). At a higher magnification, it was seen that the amount of acicular a-Ti(Zr, O) gradually decreased toward the original interface.13Lin and

Lin13indicated that the acicular a-Ti was precipitated from the

b0-Ti matrix by means of the ledge mechanism. In contrast, the reaction layer ‘‘III’’ was not found after annealing at 11001 or 13001C.

(D) Reaction Layer ‘‘IV’’ of the Ti/ZrO2Interface: The region to the nearest left of the original interface dissolved a higher concentration of Zr in Ti. No acicular a-Ti(Zr, O) was thus observed in this region as the zirconium was an effective stabilizer of b-Ti. Figures 1(b)–(d) show that a continuous

Fig. 1. Scanning electron microscopy micrographs (backscattered electron images) showing the interface of Ti and ZrO2after annealing for 6 h at (a)

11001C, (b) 13001C, (c) 14001C, and (d) 15501C. The vertical arrows in the upper side indicate the original interface. The interface reaction layers were designated as the reaction layers ‘‘I,’’ ‘‘II,’’ ‘‘III,’’ ‘‘IV,’’ ‘‘V,’’ and ‘‘VI,’’ respectively.

(3)

b0-Ti(Zr, O) layer (designated as the reaction layer ‘‘IV’’) was formed in the metal side abutting the original interface after annealing at temperatures ranging from 13001 to 15501C. No reaction layer ‘‘IV’’ was observed after annealing at 11001C as the reaction was quite limited.

(E) Reaction Layer ‘‘V’’ of the Ti/ZrO2Interface: Fig-ure 1 also demonstrates very distinct microstructFig-ures in the cer-amic side after annealing at various temperatures. At 11001C, the anneal temperature was so low that no apparent interfacial reaction was noticeable. At T 13001C, zirconia was gradually dissolved in titanium so that residual fine spherical c-ZrO2

existed in the matrix of b0-Ti(Zr, O). The spherical zirconia contained a significant amount of Y2O3, resulting in the

stabil-ization of c-ZrO2x (designated as the reaction layer ‘‘V’’) as

shown particularly in Figs. 1(c) and (d). It was believed that, at high temperatures such as 14001 or 15501C, the chemical reac-tion-enhanced dissolution of ZrO2 into Ti was an important

mechanism that dominated in the reaction layer ‘‘V.’’

Figure 4(a) shows the bright-field image (BFI) of the reaction layer ‘‘V’’ after annealing at 14001C for 6 h. The reaction layer

‘‘V,’’ in the outermost region of the original zirconia, consisted of b0-Ti(Zr, O) and c-ZrO

2x. In this layer, zirconia was

dis-solved into titanium and became rounded in shape, resulting in b-Ti with oxygen and zirconium in solid solution. As the solu-bility of yttrium (or the stabilizer of ZrO2in the present study) in

titanium was quite limited, yttrium was retained in the residual cubic zirconia. It was consistent with the results reported by Zhu et al.,5 who found that yttrium element congregated and re-mained at the interface to form a high-Y2O3content of ZrO2,

when ZrO2 reacted with molten titanium. After annealing at

15501C for 6 h, the b0-Ti(Zr, O) in the reaction layer ‘‘V’’ became an ordered phase during cooling. In Fig. 4(b), the ordered b0 -Ti(Zr, O) phase displayed a high strain-field contrast because of the lattice distortion. Figures 4(c) and (d) show the SADPs of b0 -Ti(Zr, O) with the incident electron beam along the zone axes of [021] and½112, respectively. The ordered structure was charac-terized by thef111g superlattice reflections of b0-Ti(Zr, O). In contrast, the b0-Ti(Zr, O) phase in the layer ‘‘V,’’ formed after annealing at 14001C, did not experience the order–disorder phase transformation.

(F) Reaction Layer ‘‘VI’’ of the Ti/ZrO2 Interface: At high temperatures, the oxidation–reduction reaction resulted in the formation of metastable oxygen-deficient zirconia (ZrO2x).

Then, a-Zr would be excluded from this metastable ZrO2xonto

the grain boundaries of zirconia during the subsequent cooling. In the layer ‘‘VI’’ as shown in Figs. 1(b)–(d), the a-Zr co-existed with tetragonal and/or cubic zirconia. At 13001C, the negligible grain growth of zirconia resulted in the very fine and dense a-Zr as shown in Fig. 1(b). For the sample after annealing at 14001C, zirconia grains were delineated by the continuously distributed intergranular a-Zr [Fig. 1(c)], indicating a significant degree of grain growth. In addition to the apparent grain growth of

Fig. 3. (a) Transmission electron microscopy micrograph (bright-field image) showing the reaction layer ‘‘I’’ with the coexistence of a-Ti and Ti2ZrO after annealing at 11001C/6 h. (b) selected area

dif-fraction patterns of the a-Ti and Ti2ZrO, indicating that

½0001aTi==½110Ti2ZrO and ð1010ÞaTi//ð110ÞTi2ZrO ðA ¼ ð0110ÞaTi,

B 5(1010)aTi, C¼ ð002ÞTi2ZrO, D¼ ð110ÞTi2ZrO); (c) an

energy-disper-sive spectrum of Ti2ZrO.

Fig. 2. Scanning electron microscopy micrographs (secondary electron images) showing the variation of the reaction layer ‘‘I’’ after annealing at (a) 13001C, (b) 14001C, and (c) 15501C, respectively.

(4)

zirconia, the intergranular a-Zr was coarsened and became isol-ated, as shown in Fig. 1(d), after annealing at 15501C.

In the reaction layer ‘‘VI,’’ the oxidation–reduction reaction rather than dissolution is the predominant mechanism in the reaction layer ‘‘VI.’’ The dissolution played an insignificant role in the formation of the reaction layer ‘‘VI’’ as titanium was not detected by EDS in this layer. Figures 5(a)–(d) show the BFIs of the reaction layer ‘‘VI’’ after annealing at 11001, 13001, 14001, and 15501C for 6 h, respectively. After annealing at 11001C/6 h, the limited reaction resulted in t-ZrO2x, as it was in

as-hot-pressed samples, with no intergranular a-Zr and insignificant grain growth of zirconia [Fig. 5(a)]. At 13001C/6 h, the t-ZrO2x

remained with a slight grain growth (grain size about 1–2 mm), while the dense fine a-Zr was formed by the exsolution of Zr from the metastable t-ZrO2x [Fig. 5(b)]. After annealing at

14001 or 15501C, it was found that the lenticular t-ZrO2xwith

two variants precipitated in the ordered c-ZrO2x[Figs. 5(c) and

(d)], which was stabilized by the extensive oxygen vacancies. The ordered c-ZrO2xwas recognized by the 1/5{113} superlattice

reflections. The grain sizes of zirconia after annealing at 14001

and 15501C were about 8–10 and 20–30 mm, respectively, indi-cating rapid grain growth on annealing.

The microstructures of the reaction layer ‘‘VI’’ strongly de-pended upon annealing temperature in the following respects: (1) the grain growth of zirconia; (2) the exsolution of a-Zr onto the grain boundaries of zirconia; and (3) the morphologies and crystal structures of zirconia. The microstructural features of the reaction layer ‘‘VI’’ are summarized in Table I.

It was also noted that a large amount of the pores existed in the ceramic side after annealing at T 13001C. The formation of these pores was attributed to the Kirkendall effect, because zir-conium and oxygen diffused to the titanium side much faster than titanium did toward the zirconia side in the opposite direction.

(G) Formation of the Ti3O Suboxide in a-Ti(O): In contrast to a limited diffusion range of zirconium (up to the re-action layer ‘‘I’’), oxygen showed a relatively long diffusion range (well beyond the reaction layer ‘‘I’’). Rather than forming a distinct layer with a specific thickness, the oxygen concentra-tion of a-Ti(O) decayed gradually across a wide region. During cooling, the hexagonal phases of ordered titanium suboxides such as Ti2O, Ti3O, and possibly Ti6O might be formed within

an extended range, as shown in the Ti–O phase diagram.15In

this study, only the ordered Ti3O resulted from the

transform-ation of a-Ti(O) during cooling because of the extended reaction between titanium and zirconia at 14001 or 15501C. However, no such suboxide was found in those samples after annealing at 11001 or 13001C.

Figure 6 shows that Ti3O contained stacking faults and

dis-locations in a-Ti(O) abutting the reaction layer ‘‘I’’ after an-nealing at 15501C for 6 h. The inset in the upper right corner shows the SADP of the hexagonal Ti3O with the electron beam

parallel to the zone axis of½1210. The superlattice reflections (0002),ð1011Þ, and ð2021Þ indicate that cell dimension along the c-axis of the superlattice should be twice that of the Ti cell, but not three times as proposed by Jostsons and Malin16and Lin and Lin.9The ordered structure of Ti3O observed in this study

coincided with the model proposed by Holmberg17and Yama-guchi.18It revealed that the lattice parameters of Ti

3O were a¼

ffiffiffi 3 p

aoand c 5 2co, where aoand cowere those of the Ti unit cell.

(2) Temperature Effect on Microstructural Development The microstructural development between titanium and zirconia can be explained by the isothermal Ti–Zr–O ternary phase dia-gram at 14501C, as shown in Fig. 7, because the compositions of the solid phases are approximately constant between 13001 and 15501C.19The solid, dashed, and dotted lines (marked as ‘‘1,’’ ‘‘2,’’ and ‘‘3,’’ respectively) in Fig. 7(a) are the diffusion paths, which connect all gross compositions at various cross sections along the longitudinal direction perpendicular to the interface of Ti/ZrO2on annealing at 15501, 14001, and 13001C, respectively.

The diffusion path 3 at 13001C (dotted line) crosses the fields of b-Ti, b-Ti1t-ZrO2, a-Zr1b-Ti1t-ZrO2, and a-Zr1t-ZrO2. It

is noted that the region of a-Zr1b-Ti1t-ZrO2in the Ti–Zr–O

ternary phase diagram corresponds to the interface between the layers of b-Ti1t-ZrO2and a-Zr1t-ZrO2. The reaction layers of

b-Ti, b-Ti1t-ZrO2, and a-Zr1t-ZrO2are in sequence from Ti to

ZrO2in the Ti/ZrO2diffusion couple on annealing at 13001C, as

shown on the left of Fig. 7(b). The final microstructure after cooling from 13001C is schematically shown on the right of Fig. 7(b).

The formation of b-Ti on annealing at 13001C as well as its transformation during cooling can be described as follows: on annealing at 13001C, O and Zr were dissolved into Ti, leading to the formation of b-Ti(Zr, O) in the titanium side. While O dif-fused deeply into Ti beyond the reaction layers I, resulting in a long range (up to several hundreds of micrometers) of a-Ti(O), very little Zr diffused into Ti beyond the reaction layer I. As O diffused much faster than Zr in Ti, Zr tended to accumulate in the b-Ti(Zr, O) layer (up to several tens of micrometers), causing relatively rich Zr than O in the b-Ti(Zr, O) layer. Seeing that O and Zr are the stabilizers of a and b phases, respectively, the

Fig. 4. Transmission electron microscopy micrograph (bright-field im-age) of the reaction layer ‘‘V’’ consisting of b0-Ti and c-ZrO

2xafter

annealing at (a) 14001C/6 h; (b) at 15501C/6 h; (c) a selected area dif-fraction pattern of b0-Ti in Fig. 4(b) (zone axis is [021], A¼ ð200Þ,

B¼ ð222Þ, and C ¼ ð111Þ); (d) an SADP of b0-Ti in Fig. 4(b) (zone axis

is½112, A ¼ ð132Þ, B ¼ ð110Þ, and C ¼ ð111ÞÞ.

(5)

b-Ti(Zr, O) with a high concentration ( 30 wt% in this study) of Zr remained as a distorted b phase (designated as b0) during cooling, but transformed into the a phase otherwise. In the fact that the b-Ti(Zr, O) layer was relatively rich with Zr at 13001C, as indicated by the diffusion path 3 in Fig. 7(a), layer IV (b0) rather than layer III (a1b) was observed after cooling.

The reaction layer III existed in the interface after annealing at 14001C, but not at 13001C. As the b-Ti(Zr, O) formed on annealing had relatively rich O at 14001C than at 13001C, as

compared with diffusion paths 2 and 3, two cases took place in the b-Ti(Zr, O) during cooling from 14001C: (1) the Zr concentration away from the original interface was so low that the acicular a phase was precipitated along with b0(layer III); and (2) the Zr concentration close to the original interface was high enough that the b phase was stabilized and the phase transformation of b-b0occurred (layer IV).

Fig. 5. Transmission electron microscopy micrograph (bright-field image) of the reaction layer ‘‘VI’’ far away from the original interface after annealing at (a) 11001C, (b) 13001C, (c) 14001C, and (d) 15501C, respectively, for 6 h.

Table I. Zirconia and Intergranulara-Zr in the Reaction Layer ‘‘VI’’

Annealing conditions

Grain growth of zirconia and its

size Intergranular a-Zr Morphology and crystal structure of zirconia 11001C/6 h Insignificant about 0.3–0.4 mm

Not found Equiaxed

t-ZrO2x 13001C/6 h Insignificant about 1–2 mm Fine and dense Equiaxed t-ZrO2x 14001C/6 h Significant about 8–10 mm Continuously distributed on grain boundaries t-ZrO2x (lenticular)1 ordered c-ZrO2x 15501C/6 h Significant about 20 –30 mm Isolated and coarsened on grain boundaries t-ZrO2x (lenticular)1 ordered c-ZrO2x

Fig. 6. Transmission electron microscopy micrograph (bright-field im-age) of the suboxide Ti3O near the reaction layer ‘‘I’’ after annealing at

15501C for 6 h; the inset SADP of Ti3O along the½1210 zone axis

(A 5 (0004), B¼ ð3030Þ, C ¼ ð1011Þ, and D ¼ ð2021Þ).

(6)

The zirconia in the Ti–Zr–O ternary phase diagram, shown in Fig. 7(a), would be in the cubic phase instead of the tetragonal phase when the Ti/ZrO2diffusion couple was isothermally

an-nealed at temperatures above 14001C, because of the dissolution of the stabilizer yttria. In the ceramic side, t-ZrO2x, ordered

c-ZrO2x, and intergranular a-Zr existed in the reaction layer

‘‘VI’’ after annealing at 14001C. The microstructures developed on annealing at 14001C and after subsequent cooling are sche-matically shown in Fig. 7(c).

Figure 7(a) reveals that the solid line or the diffusion path 1 at 15501C crosses the fields of b-Ti, a-Ti1b-Ti, b-Ti, b-Ti1c-ZrO2,

a-Zr1b-Ti1c-ZrO2, and a-Zr1c-ZrO2. The reaction layers of

b-Ti, a-Ti1b-Ti, b-Ti, b-Ti1c-ZrO2, and a-Zr1c-ZrO2would be

observed in the Ti–ZrO2diffusion couple on annealing at 15501C

as shown on the left of Fig. 7(d). By comparing various diffusion paths, it is worth noting that the two-phase a-Ti(Zr, O)1b-Ti

(Zr, O) region, where the diffusion path passes through, is found neither at 13001 nor at 14001C. This region is corresponding to the reaction layer ‘‘II’’ in Fig. 1(d), consisting of b0-Ti and the lamellar Ti2ZrO1a-Ti. The microstructural development on

annealing at 15501C and after subsequent cooling has been de-scribed previously11,13and schematically shown in Fig. 7(d).

It was worth noting that there existed a wide a-Ti(O) solid solution region, neighboring the reaction unaffected Ti, in all the diffusion couples after annealing at temperatures ranging from 11001 to 15501C. As the relative concentration of oxygen was much larger than that of Zr in this a-Ti(O) solid solution region, all the diffusion paths near the Ti corner of the Ti–Zr–O ternary phase diagram should be bowed to the Ti–O edge as Fig. 7(a) indicated.

According to the foregoing discussion, the reaction layers formed in the interface of titanium and zirconia at various

Fig. 7. Schematic diagrams showing the microstructural evolution and diffusion paths of the Ti/ZrO2diffusion couple annealed at various

tempera-tures. (a) Various diffusion paths in the Ti–Zr–O phase diagram19; (b)–(d) the microstructures of Ti/ZrO

2diffusion couple on annealing at 13001, 14001,

and 15501C and after subsequent cooling, respectively.

(7)

temperatures are summarized in Table II. In brief, a very limited interfacial reaction took place at temperatures as low as 11001C, merely leading to the formation of the a-Ti(O) and oxygen-de-ficient zirconia t-ZrO2x. In the titanium side, a thin a-Ti(O)1 Ti2ZrO layer (or layer I) existed after annealing at T 11001C;

the b0-Ti(Zr, O) layer (or layer IV) was formed after annealing at T 13001C; a two-phase a-Ti(O)1b0-Ti(Zr, O) layer (or layer III) was observed after annealing at T 14001C; and a three-phase Ti2ZrO1a-Ti(O, Zr)1b0-Ti (O, Zr) layer (or layer II) was

found after annealing at 15501C. In the zirconia side, near the original interface (or layer V), b0-Ti co-existed with fine spherical c-ZrO2x, which dissolved a significant amount of Y2O3in solid

solution at T 13001C. Further into the ceramic side (or layer VI), the zirconia grains grew significantly with the lenticular t-ZrO2x, being precipitated in the c-ZrO2x matrix at

T 14001C. However, no cubic zirconia was found in the re-action layer ‘‘VI’’ after annealing at 11001 or 13001C. The ex-solution of Zr out of the metastable ZrO2xled to the formation

of a-Zr, which was finely dense after annealing at 13001C, con-tinuously distributed along grain boundaries at 14001C, and be-came coarsened at 15501C. It is also noted that the suboxide Ti3O was found in the a-Ti(O), to the left of the reaction layer

‘‘I,’’ after annealing at 14001 and 15501C, while an ordered b0 -Ti(Zr, O) phase existed in the reaction layer ‘‘V’’ after annealing at 15501C.

IV. Conclusions

(1) The diffusional reactions between titanium and zirconia were carried out isothermally in argon at temperatures ranging from 11001 to 15501C for 6 h. It was found that the microstruc-ture in the Ti/ZrO2interface strongly depended on the annealing

temperature.

(2) In the titanium side, a thin a-Ti(O)1Ti2ZrO layer (or

layer I) existed after annealing at T 11001C; the b0-Ti(Zr, O) layer (or layer IV) was formed after annealing at T 13001C; a two-phase a-Ti(O)1b0-Ti(Zr, O) layer (or layer III) was ob-served after annealing at T 14001C; and a three-phase Ti2

Z-rO1a-Ti(O, Zr)1b0-Ti (O, Zr) layer (or layer II) was found after annealing at 15501C.

(3) In the zirconia side near the original interface, b0-Ti co-existed with fine spherical c-ZrO2x, which dissolved a signifi-cant amount of Y2O3in solid solution at temperatures ranging

from 13001 to 15501C, due to the reaction-enhanced dissolution mechanism.

(4) Further into the ceramic side, the zirconia grain grew significantly at 14001 and 15501C. a-Zr was excluded out of the metastable ZrO2xafter annealing T 13001C: a-Zr was

dense-ly distributed along with t-ZrO2x at 13001C, continuously

located at 14001C, and became coarsened at 15501C. The len-ticular t-ZrO2xwas precipitated in c-ZrO2xafter annealing at

14001 and 15501C, while the limited reaction resulted in t-ZrO2xas it was in as-hot-pressed samples after annealing at

11001 or 13001C.

(5) Finally, the microstructural development in the Ti/ZrO2

annealed at various temperatures was described by the aid of the Ti–Zr–O ternary phase diagram.

Acknowledgments

The authors would like to express their sincere appreciation to Mr. Chi-Ming Wen at Chung-Shan Institute of Science and Technology for preparing the hot-pressed specimens.

References 1

G. Economos and W. D. Kingery, ‘‘Metal–Ceramic Interactions: II, Metal Oxide Interfacial Reactions at Elevated Temperatures,’’ J. Am. Ceram. Soc., 36 [12] 403–9 (1953).

2

B. C. Weber, W. M. Thompson, H. O. Bielstein, and M. A. Schwartz, ‘‘Cer-amic Crucible for Melting Titanium,’’ J. Am. Ceram. Soc., 40 [11] 363–73 (1957).

3

R. Ruh, ‘‘Reaction of Zirconia and Titanium at Elevated Temperatures,’’ J. Am. Ceram. Soc., 46 [7] 301–6 (1963).

4

R. Ruh, N. M. Tallan, and H. A. Lipsitt, ‘‘Effect of Metal Additions on the Microstructure of Zirconia,’’ J. Am. Ceram. Soc., 47 [12] 632–5 (1964).

5

J. Zhu, A. Kamiya, T. Yamada, W. Shi, K. Naganuma, and K. Mukai, ‘‘Sur-face Tension, Wettability, and Reactivity of Molten Titanium in Ti/Yttria-Stabil-ized Zirconia System,’’ Mater. Sci. Eng. A, A327, 117–27 (2002).

6

B. C. Weber, H. J. Garrett, F. A. Mauer, and M. A. Schwartz, ‘‘Obser-vations on the Stabilization of Zirconia,’’ J. Am. Ceram. Soc., 39 [6] 197–207 (1956).

7

C. L. Lin, D. Gan, and P. Shen, ‘‘Stabilization of Zirconia Sintered with Ti-tanium,’’ J. Am. Ceram. Soc., 71 [8] 624–9 (1988).

8

K. F. Lin and C. C. Lin, ‘‘Interfacial Reactions Between Zirconia and Titan-ium,’’ Scr. Metall., 39 [10] 1333–8 (1998).

9

K. F. Lin and C. C. Lin, ‘‘Transmission Electron Microscope Investigation of the Interface Between Titanium and Zirconia,’’ J. Am. Ceram. Soc., 82 [11] 3179– 85 (1999).

10

K. F. Lin and C. C. Lin, ‘‘Interfacial Reactions Between Ti–6Al–4V Alloy and Zirconia Mold During Casting,’’ J. Mater. Sci., 34, 5899–906 (1999).

11

K. L. Lin and C. C. Lin, ‘‘Ti2ZrO Phases Formed in the Titanium and

Zir-conia Interface after Reaction at 15501C,’’ J. Am. Ceram. Soc., 88 [5] 1268–72 (2005).

12

K. L. Lin and C. C. Lin, ‘‘Zirconia-Related Phases in the Zirconia/Titanium Diffusion Couple after Annealing at 11001 to 15501C,’’ J. Am. Ceram. Soc., 88 [10] 2928–34 (2005).

13

K. L. Lin and C. C. Lin, ‘‘Microstructural Evolution and Formation Mech-anism of the Interface Between Zirconia and Titanium Annealed at 15501C,’’ J. Am. Ceram. Soc., 89 [4] 1400–8 (2006).

14

G. Cliff and G. W. Lorimer, ‘‘The Quantitative Analysis of Thin Specimens,’’ J. Microsc., 130 [3] 203–7 (1975).

15

J. L. Murray and H. A. Wriedt, ‘‘The Oxygen–Titanium System’’; pp. 211–29 in Phase Diagrams of Binary Titanium Alloys, Edited by J. L. Murray. ASM International, Metals Park, OH, 1987.

16

A. Jostsons and A. S. Malin, ‘‘The Ordered Structure of Ti3O,’’ Acta Cryst.,

B24 [4] 211–3 (1968).

17

B. Holmberg, ‘‘Disorder and Order in Solid Solution of Oxygen in a-Titan-ium,’’ Acta Chem. Scand., 16, 1245–50 (1962).

18

S. Yamaguchi, ‘‘Interstitial Order–Disorder Transformation in the Ti–O Solid Solution. I. Ordered Arrangement of Oxygen,’’ J. Phys. Soc. Jpn., 27 [1] 155–63 (1969).

19

M. Hoch, R. L. Dean, C. K. Hwu, and S. M. Wolosin, ‘‘Zirconium Plus Oxygen Plus Another Metal’’; p. 12 in Phase Diagrams for Zirconium and Zirconia Systems, Edited by H. M. Ondik and H. F. McMurdie. American Ceramic

So-ciety, Westerville, OH, 1998. &

Table II. Reaction Layers Formed in the Interface of Ti/ZrO2at Various Temperatures

Phases Reaction layers 11001C 13001C 14001C 15501C

Metal side a-Ti(O)





m m

a-Ti(Zr, O)1Ti2ZrO I









a-Ti(Zr, O)1Ti2ZrO1b0-Ti(Zr, O) II x x x



a-Ti(Zr, O)1b0-Ti(Zr, O) III x x





b0-Ti(Zr, O) IV x







Ceramic side b0-Ti(Zr, O)1c-ZrO

2x V x





#

a-Zr(O)1t-ZrO2x1c-ZrO2x VI x w





t-ZrO2x











, observed; x, none; m, with sparsely distributed Ti3O; #, with ordered b0-Ti(Zr, O); w, no c-ZrO2xwas observed. 2

數據

Figure 2 displays the SEIs of the lamellar a-Ti (Zr, O) and Ti 2 ZrO in the reaction layer ‘‘I’’ etched by Kroll reagent (10 mL
Fig. 3. (a) Transmission electron microscopy micrograph (bright-field image) showing the reaction layer ‘‘I’’ with the coexistence of a-Ti and Ti 2 ZrO after annealing at 11001C/6 h
Figure 6 shows that Ti 3 O contained stacking faults and dis-
Fig. 6. Transmission electron microscopy micrograph (bright-field im- im-age) of the suboxide Ti 3 O near the reaction layer ‘‘I’’ after annealing at
+3

參考文獻

相關文件

However, to closely respond to various contextual changes locally and globally, more attention is given to the development of personal attributes expected of our students

In response to the changing needs of society, the rapid development of science and technology, the views of stakeholders collected through various surveys and

In response to the changing needs of society, the rapid development of technology, views of stakeholders collected through various engagement activities and events

Wang, Solving pseudomonotone variational inequalities and pseudocon- vex optimization problems using the projection neural network, IEEE Transactions on Neural Networks 17

Define instead the imaginary.. potential, magnetic field, lattice…) Dirac-BdG Hamiltonian:. with small, and matrix

Akira Hirakawa, A History of Indian Buddhism: From Śākyamuni to Early Mahāyāna, translated by Paul Groner, Honolulu: University of Hawaii Press, 1990. Dhivan Jones, “The Five

Master Taixu has always thought of Buddhist arts as important, the need to protect Buddhist arts, and using different forms of method to propagate the Buddha's teachings.. However,

Continue to serve as statements of curriculum intentions setting out more precisely student achievement as a result of the curriculum.