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Hardening behavior of Pt–Ti microalloys
Journal of Alloys and Compounds 645 (2015) 34–37
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom
Hardening behavior of Pt–Ti microalloys Yi-min Guan, Si-yong Xu, Jin-xin Guo, Guo-yi Qin ⇑ The Key Laboratory of Micro-nano Materials and Technology, Department of Materials Science and Engineering, Yunnan University, Kunming 650091, China
a r t i c l e
i n f o
Article history: Received 2 January 2015 Received in revised form 21 April 2015 Accepted 22 April 2015 Available online 27 April 2015 Keywords: Pt–Ti microalloys Thermomechanical processing Hardening Hardness measurement Electron microscopy
a b s t r a c t Microalloys of platinum containing 0.3 or 0.5 wt% titanium (Pt–0.3Ti and Pt–0.5Ti, respectively) were studied to determine their solid solution hardening, age hardening, work hardening, and annealing softening behavior. The obtained results revealed that the solid solution hardening and work hardening effects are both quite significant. The quenching hardness (114 HV), processing hardness (202 HV with 90% rolling), and annealing hardness (130 HV after 1 h at 800 °C) of the Pt–0.5Ti microalloy are 1.7, 2.0, and 2.6 times greater, respectively, than that of pure Pt. The work hardening curves of the aged microalloys were also unique in that a deformation of 20–70% produced no discernible work hardening of the microalloys. Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction Platinum (Pt) has been widely used as an electrode material in electrochemistry and biological medicine and as a structural component in jewelry [1,2] owing to its excellent oxidation resistance, chemical corrosion resistance, and plasticity; however, its low hardness limits the effective applications in the above areas and other aspects. The development of dispersion-strengthened alloys with excellent high-temperature mechanical properties, such as Pt–ZrO2 and Pt–Y2O3, has allowed the use of Pt in high-temperature devices [3–5]. However, such alloys are quite complex to produce, and their room-temperature hardness is poor compared to pure Pt. van der Lingen et al. [6] studied the hardening of Pt-alloys containing 2–4 wt% of various elements (Ti, Zr, V, Ge, Ga, Ta, W, In, Sn, etc.) and found that a dilute Pt–Ti alloy provides sufficient room-temperature strength for use in jewelry. Similarly, Lang et al. found that ordered phases such as Pt7Cu [7] and Pt8Cr(V) [8], which are formed through the deformation aging of dilute Pt–Cu and Pt–Cr(V) alloys, respectively, have a sufficient hardening effect on the Pt matrix for its potential use in jewelry. However, the required level of alloying reduces the chemical corrosion resistance below acceptable levels for biomedical electrode materials. ⇑ Corresponding author at: The Key Laboratory of Micro-nano Materials and Technology, Department of Materials Science and Engineering, Yunnan University, Cuihu North Road No. 2, Kunming 650091, China. Tel./fax: +86 0871 65931533. E-mail addresses: [email protected] (Y.-m. Guan), [email protected] (S.-y. Xu), [email protected] (J.-x. Guo), [email protected] (G.-y. Qin). http://dx.doi.org/10.1016/j.jallcom.2015.04.152 0925-8388/Ó 2015 Elsevier B.V. All rights reserved.
The Pt8Ti superlattice structure [9–12] can be formed in dilute Pt–Ti–(Zr, Hf, Ta, Cr, V, W, Mo) alloys by solid solution aging or deformation aging. However, the effect of adding very small amounts of Ti, Zr, Hf, or Ta on the hardening behavior of Pt has rarely been studied or reported. This study considers the solid solution hardening, work hardening, age hardening, and annealing softening of Pt–Ti microalloys. New microalloy will be expected to be applied to the biological electrodes and jewelry and so on. 2. Experimental procedure Buttons of Pt (30 g each) microalloyed with 0.3 or 0.5 wt% Ti (Pt–0.3Ti and Pt–0.5Ti, respectively) were prepared by melting the required quantities of both elements (99.95% purity) under an Ar atmosphere in a vacuum arc furnace. Each button was re-melted twice to promote homogeneity and then cold-rolled to reduce the thickness by 50%. A solid solution treatment was then applied: the samples were heated to 1000 °C for 1 h in a vacuum resistance furnace and were quenched in water. Work hardening experiments were performed by treating the samples with solid solution at 1000 °C for 1 h or by aging the solution-treated samples at 450 °C for 1 h, followed by cold rolling to obtain a 10–90% reduction in thickness. The samples that were cold-rolled to a 90% reduction in thickness were subsequently used for annealing softening tests by heating to 400–800 °C for 1 h. The hardness of the Pt–Ti microalloys was measured using a Vickers hardness tester with a 0.2-kg load and a holding time of 15 s. For the hardness measurements, one specimen was used for each experimental condition, and five points were measured for each specimen. The hardness data in the paper are the average of the five measurements, and standard deviation for each condition are all between plus or minus 5. Specimens for reflected light microscopy were first mechanically polished and then electrolytically etched in a solution containing 25 ml of HCl and 25 g of NaCl in 65 ml of distilled water using a 10-V alternating current for 50–60 s and a graphite electrode. For transmission electron microscopy (TEM), specimens were
Y.-m. Guan et al. / Journal of Alloys and Compounds 645 (2015) 34–37 Table 1 Solid solution hardening and age hardening behavior of the microalloys.
35
3. Results and discussion
Temp. (°C)/time (h)
Pt–0.3Ti-microhardness (HV)
Pt–0.5Ti-microhardness (HV)
3.1. Hardening by solid solution and aging
1000/1 350/10 400/1 400/3 400/5 450/0.5 450/1 450/3 450/5 500/1 500/2 500/3 500/5
84 ± 5 89 ± 5 79 ± 5 87 ± 5 88 ± 5 89 ± 5 91 ± 5 89 ± 5 90 ± 5 87 ± 5 88 ± 5 87 ± 5 86 ± 5
114 ± 5 107 ± 5 104 ± 5 108 ± 5 107 ± 5 108 ± 5 111 ± 5 111 ± 5 110 ± 5 108 ± 5 110 ± 5 107 ± 5 108 ± 5
The microhardnesses of the Pt–0.3Ti and Pt–0.5Ti microalloys in a solid solution state were found to be 84 and 114 HV, respectively, representing a significant increase over the 50 HV microhardness of cast Pt. This indicates that adding a small amount of Ti to Pt has a significant effect on solid solution strengthening. Moreover, although the Pt–Ti microalloy is in a completely disordered solid solution state at high temperatures, low-temperature aging is capable of generating an ordered Pt8Ti phase [9]. Despite this, Table 1 shows that there was very little change in the microhardness of the quenched microalloys with aging, which suggests that this level of Ti addition is insufficient to produce any significant effect on the age hardening. This microalloy behavior can possibly be explained by the fact that Ti and Pt have very similar atomic radii (0.145 and 0.139 lm, respectively) with very different electronegativities (1.54 and 2.28 V, respectively). In other words, the 0.74 V electronegativity difference is a key factor in the very large solid solution hardening effect. However, unlike Pt–11 at%Cr(V) dilute alloys that have a very strong age hardening effect [8], the Pt8Ti ordered phase [9] formed in the Pt–Ti microalloys is insufficient to create a noticeable dispersion strengthening effect. 3.2. Work hardening
Fig. 1. Influence of cold rolling deformation on the microhardness of as-quenched and aged Pt–Ti microalloys.
prepared by first grinding the samples from 200 to 100 lm in thickness and then dimpling to reduce the thickness to 30 lm. Thin foil specimens were prepared by punching 3-mm diameter discs, followed by chemical polishing and Ar+-ion milling in a precision ion polishing system (PIPS, Gatan) operating at an accelerating voltage of 4.5 kV and an incident angle of 2–8°. All TEM examinations were performed using a JEM-2100 instrument operating at 200 kV.
The work hardening curves of the quenched (1000 °C for 1 h) samples in Fig. 1 show that work hardening increases linearly with the extent of rolling deformation, reaching a maximum at 90% reduction with 154 HV (Pt–0.3Ti) and 183 HV (Pt–0.5Ti). The work hardening curves (Fig. 1) of the aged microalloy samples at 450 °C for 1 h were unusual. The hardness values showed a rapid increase for a rolling deformation of less than 20%, remained essentially unchanged for further deformation up to 70%, and beyond 70%, rapidly increased to reach maximum values of 184 and 202 HV for Pt–0.3Ti and Pt–0.5Ti, respectively, at 90% deformation. Fig. 1 also shows that the work hardening of the Pt–0.5Ti alloy is more pronounced than that of Pt–0.3Ti and that the work hardening is greater in aged alloys than quenched alloys. Metallographic examination found the severely deformed specimens to have a typical cold-rolled structure (Fig. 2), which consisted of a large number of linear dislocations. More importantly, a greater dislocation density is clearly produced by deformation
Fig. 2. Microstructure of quenched and aged Pt–0.5Ti microalloys after cold rolling deformation of 90%.
36
Y.-m. Guan et al. / Journal of Alloys and Compounds 645 (2015) 34–37
Fig. 3. Influence of annealing on the microhardnesses of 90% cold-rolled microalloys.
in the aged microalloy, indicating a greater extent of work hardening. The lack of change in the hardness of the aged microalloys in the deformation range of 20–70% is therefore attributed to the existence of the Pt8Ti ordered phase [9], creating a balance between the increase and decrease in dislocations during rolling.
3.3. Annealing softening by rolling deformation Fig. 3 shows the annealing softening curves of the samples that were aged at 450 °C for 1 h and deformed by 90%, in which it is
evident that an annealing temperature of less than 450 °C has virtually no effect on the hardness. With annealing at 500 °C, the hardness begins to decrease but only by about 6%. Indeed, even with annealing at 700 and 800 °C for 1 h, the microhardnesses of the Pt–0.5Ti alloy was still 3.2 and 2.6 times greater, respectively, than the 50 HV microhardness of Pt. In the Pt–0.3Ti alloy, these values dropped slightly to 2.4 and 2.0 times, respectively, greater than the microhardness of pure Pt. Thus, the Pt–0.5Ti alloy has greater annealing hardness and annealing stability of the considered microalloys. The TEM images in Fig. 4 show that annealing at 500 °C for 1 h partly transforms the microstructure of the deformed (90%) Pt–0.5Ti alloy into a low-angle grain boundary structure, but the dislocation density in the alloy remains high. Because this high dislocation density could effectively prevent recrystallization, it provides an explanation for the slight reduction in the microhardness of the deformed alloy. After annealing at 700 °C for 1 h, the structure is almost fully recrystallized; however, the existence of short dislocations within this crystalline structure helps it retain much of its hardness. Observation by optical microscopy (Fig. 5) revealed that the sample annealed at 800 °C for 1 h was fully recrystallized, which corresponds to the significant reduction in its hardness. 4. Conclusions The microalloying of Pt with small amounts (0.3–0.5 wt%) of Ti has been shown to have a significant solid solution strengthening and process hardening effect, resulting in almost no change in hardness after aging over a very large range of deformation by cold rolling (20–70%). This is due to the fact that the amount of ordered
Fig. 4. The TEM images of rolled (90%) Pt–0.5Ti microalloy after annealing at 500 °C and 700 °C for 1 h.
Fig. 5. Optical images (400) of rolled (90%) Pt–0.5Ti microalloy under different annealing conditions: (a) the partial recrystallized microstructure after annealing at 700 °C for 1 h and (b) the fully recrystallized microstructure after annealing at 800 °C for 1 h.
Y.-m. Guan et al. / Journal of Alloys and Compounds 645 (2015) 34–37
Pt8Ti phase being formed is insufficient to have any significant aging hardening effect. Moreover, the hardnesses of these Pt–Ti microalloys remain relatively high even after recrystallization by annealing, suggesting they have good potential for use as a biomedical electrode material or in jewelry. Acknowledgment The authors would like to thank the National Natural Science Foundation of China (Award No. 51164034) for the financial support provided for this research. References [1] B.K. Woodward, Platinum group metals for permanent implantable electronic devices, in: Niklaus Baltzer, Thierry Copponnex (Eds.), Precious Metals for Biomedical Applications, Woodhead Publishing, 2014, pp. 130–147.
37
[2] Y.T. Ning, Z.F. Yang, F. Wen, Platinum New Application Field, Metallurgical Industry Press of China, Platinum, 2010. [3] N. Sekido, A. Hoshino, M. Fukuzaki, Y. Yamabe-Mitarai, T. Maruko, Steady state creep behavior of zirconia dispersion strengthened platinum alloys, Mater. Sci. Eng. A 528 (2011) 8451–8459. [4] K. Maruyama, H. Yamasaki, T. Hamada, High-temperature creep of GTH (Gottsu-Tsuyoi-Hakkin), Mater. Sci. Eng. A 510–511 (2009) 312–316. [5] M. Besterci, P. Hvizdoš, K. Sülleiová, C. Edtmaier, Processing, microstructure and creep testing of Pt–Y2O3 composites, Mater. Des. 28 (2007) 2540–2543. [6] T. Biggs, S.S. Taylor, E. van der Lingen, The hardening of platinum alloys for potential jewellery application, Platinum Met. Rev. 49 (2005) 2–15. [7] S. Nxumalo, M.P. Nzula, C.I. Lang, Order hardening of Pt8X alloys, Mater. Sci. Eng. A 445–446 (2007) 336–340. [8] M. Carelse, C.I. Lang, Order hardening in platinum 14 at.% copper, Scripta Mater. 54 (2006) 1311–1315. [9] P. Pietrokowsky, Novel ordered phase, Pt8Ti, Nature 206 (1965) 291. [10] K.P. Mabunda, C.I. Lang, The Pt8Zr ordering transformation, J. Alloys Comp. 613 (2014) 375–378. [11] S. Nxumalo, C.I. Lang, Thermodynamic stability of Pt8V, J. Alloys Comp. 425 (2006) 181–184. [12] M.P. Nzula, C.I. Lang, D.J.H. Cockayne, The formation of Pt8Cr in Pt 10 at.% Cr, J. Alloys Comp. 420 (2006) 165–170.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom
Hardening behavior of Pt–Ti microalloys Yi-min Guan, Si-yong Xu, Jin-xin Guo, Guo-yi Qin ⇑ The Key Laboratory of Micro-nano Materials and Technology, Department of Materials Science and Engineering, Yunnan University, Kunming 650091, China
a r t i c l e
i n f o
Article history: Received 2 January 2015 Received in revised form 21 April 2015 Accepted 22 April 2015 Available online 27 April 2015 Keywords: Pt–Ti microalloys Thermomechanical processing Hardening Hardness measurement Electron microscopy
a b s t r a c t Microalloys of platinum containing 0.3 or 0.5 wt% titanium (Pt–0.3Ti and Pt–0.5Ti, respectively) were studied to determine their solid solution hardening, age hardening, work hardening, and annealing softening behavior. The obtained results revealed that the solid solution hardening and work hardening effects are both quite significant. The quenching hardness (114 HV), processing hardness (202 HV with 90% rolling), and annealing hardness (130 HV after 1 h at 800 °C) of the Pt–0.5Ti microalloy are 1.7, 2.0, and 2.6 times greater, respectively, than that of pure Pt. The work hardening curves of the aged microalloys were also unique in that a deformation of 20–70% produced no discernible work hardening of the microalloys. Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction Platinum (Pt) has been widely used as an electrode material in electrochemistry and biological medicine and as a structural component in jewelry [1,2] owing to its excellent oxidation resistance, chemical corrosion resistance, and plasticity; however, its low hardness limits the effective applications in the above areas and other aspects. The development of dispersion-strengthened alloys with excellent high-temperature mechanical properties, such as Pt–ZrO2 and Pt–Y2O3, has allowed the use of Pt in high-temperature devices [3–5]. However, such alloys are quite complex to produce, and their room-temperature hardness is poor compared to pure Pt. van der Lingen et al. [6] studied the hardening of Pt-alloys containing 2–4 wt% of various elements (Ti, Zr, V, Ge, Ga, Ta, W, In, Sn, etc.) and found that a dilute Pt–Ti alloy provides sufficient room-temperature strength for use in jewelry. Similarly, Lang et al. found that ordered phases such as Pt7Cu [7] and Pt8Cr(V) [8], which are formed through the deformation aging of dilute Pt–Cu and Pt–Cr(V) alloys, respectively, have a sufficient hardening effect on the Pt matrix for its potential use in jewelry. However, the required level of alloying reduces the chemical corrosion resistance below acceptable levels for biomedical electrode materials. ⇑ Corresponding author at: The Key Laboratory of Micro-nano Materials and Technology, Department of Materials Science and Engineering, Yunnan University, Cuihu North Road No. 2, Kunming 650091, China. Tel./fax: +86 0871 65931533. E-mail addresses: [email protected] (Y.-m. Guan), [email protected] (S.-y. Xu), [email protected] (J.-x. Guo), [email protected] (G.-y. Qin). http://dx.doi.org/10.1016/j.jallcom.2015.04.152 0925-8388/Ó 2015 Elsevier B.V. All rights reserved.
The Pt8Ti superlattice structure [9–12] can be formed in dilute Pt–Ti–(Zr, Hf, Ta, Cr, V, W, Mo) alloys by solid solution aging or deformation aging. However, the effect of adding very small amounts of Ti, Zr, Hf, or Ta on the hardening behavior of Pt has rarely been studied or reported. This study considers the solid solution hardening, work hardening, age hardening, and annealing softening of Pt–Ti microalloys. New microalloy will be expected to be applied to the biological electrodes and jewelry and so on. 2. Experimental procedure Buttons of Pt (30 g each) microalloyed with 0.3 or 0.5 wt% Ti (Pt–0.3Ti and Pt–0.5Ti, respectively) were prepared by melting the required quantities of both elements (99.95% purity) under an Ar atmosphere in a vacuum arc furnace. Each button was re-melted twice to promote homogeneity and then cold-rolled to reduce the thickness by 50%. A solid solution treatment was then applied: the samples were heated to 1000 °C for 1 h in a vacuum resistance furnace and were quenched in water. Work hardening experiments were performed by treating the samples with solid solution at 1000 °C for 1 h or by aging the solution-treated samples at 450 °C for 1 h, followed by cold rolling to obtain a 10–90% reduction in thickness. The samples that were cold-rolled to a 90% reduction in thickness were subsequently used for annealing softening tests by heating to 400–800 °C for 1 h. The hardness of the Pt–Ti microalloys was measured using a Vickers hardness tester with a 0.2-kg load and a holding time of 15 s. For the hardness measurements, one specimen was used for each experimental condition, and five points were measured for each specimen. The hardness data in the paper are the average of the five measurements, and standard deviation for each condition are all between plus or minus 5. Specimens for reflected light microscopy were first mechanically polished and then electrolytically etched in a solution containing 25 ml of HCl and 25 g of NaCl in 65 ml of distilled water using a 10-V alternating current for 50–60 s and a graphite electrode. For transmission electron microscopy (TEM), specimens were
Y.-m. Guan et al. / Journal of Alloys and Compounds 645 (2015) 34–37 Table 1 Solid solution hardening and age hardening behavior of the microalloys.
35
3. Results and discussion
Temp. (°C)/time (h)
Pt–0.3Ti-microhardness (HV)
Pt–0.5Ti-microhardness (HV)
3.1. Hardening by solid solution and aging
1000/1 350/10 400/1 400/3 400/5 450/0.5 450/1 450/3 450/5 500/1 500/2 500/3 500/5
84 ± 5 89 ± 5 79 ± 5 87 ± 5 88 ± 5 89 ± 5 91 ± 5 89 ± 5 90 ± 5 87 ± 5 88 ± 5 87 ± 5 86 ± 5
114 ± 5 107 ± 5 104 ± 5 108 ± 5 107 ± 5 108 ± 5 111 ± 5 111 ± 5 110 ± 5 108 ± 5 110 ± 5 107 ± 5 108 ± 5
The microhardnesses of the Pt–0.3Ti and Pt–0.5Ti microalloys in a solid solution state were found to be 84 and 114 HV, respectively, representing a significant increase over the 50 HV microhardness of cast Pt. This indicates that adding a small amount of Ti to Pt has a significant effect on solid solution strengthening. Moreover, although the Pt–Ti microalloy is in a completely disordered solid solution state at high temperatures, low-temperature aging is capable of generating an ordered Pt8Ti phase [9]. Despite this, Table 1 shows that there was very little change in the microhardness of the quenched microalloys with aging, which suggests that this level of Ti addition is insufficient to produce any significant effect on the age hardening. This microalloy behavior can possibly be explained by the fact that Ti and Pt have very similar atomic radii (0.145 and 0.139 lm, respectively) with very different electronegativities (1.54 and 2.28 V, respectively). In other words, the 0.74 V electronegativity difference is a key factor in the very large solid solution hardening effect. However, unlike Pt–11 at%Cr(V) dilute alloys that have a very strong age hardening effect [8], the Pt8Ti ordered phase [9] formed in the Pt–Ti microalloys is insufficient to create a noticeable dispersion strengthening effect. 3.2. Work hardening
Fig. 1. Influence of cold rolling deformation on the microhardness of as-quenched and aged Pt–Ti microalloys.
prepared by first grinding the samples from 200 to 100 lm in thickness and then dimpling to reduce the thickness to 30 lm. Thin foil specimens were prepared by punching 3-mm diameter discs, followed by chemical polishing and Ar+-ion milling in a precision ion polishing system (PIPS, Gatan) operating at an accelerating voltage of 4.5 kV and an incident angle of 2–8°. All TEM examinations were performed using a JEM-2100 instrument operating at 200 kV.
The work hardening curves of the quenched (1000 °C for 1 h) samples in Fig. 1 show that work hardening increases linearly with the extent of rolling deformation, reaching a maximum at 90% reduction with 154 HV (Pt–0.3Ti) and 183 HV (Pt–0.5Ti). The work hardening curves (Fig. 1) of the aged microalloy samples at 450 °C for 1 h were unusual. The hardness values showed a rapid increase for a rolling deformation of less than 20%, remained essentially unchanged for further deformation up to 70%, and beyond 70%, rapidly increased to reach maximum values of 184 and 202 HV for Pt–0.3Ti and Pt–0.5Ti, respectively, at 90% deformation. Fig. 1 also shows that the work hardening of the Pt–0.5Ti alloy is more pronounced than that of Pt–0.3Ti and that the work hardening is greater in aged alloys than quenched alloys. Metallographic examination found the severely deformed specimens to have a typical cold-rolled structure (Fig. 2), which consisted of a large number of linear dislocations. More importantly, a greater dislocation density is clearly produced by deformation
Fig. 2. Microstructure of quenched and aged Pt–0.5Ti microalloys after cold rolling deformation of 90%.
36
Y.-m. Guan et al. / Journal of Alloys and Compounds 645 (2015) 34–37
Fig. 3. Influence of annealing on the microhardnesses of 90% cold-rolled microalloys.
in the aged microalloy, indicating a greater extent of work hardening. The lack of change in the hardness of the aged microalloys in the deformation range of 20–70% is therefore attributed to the existence of the Pt8Ti ordered phase [9], creating a balance between the increase and decrease in dislocations during rolling.
3.3. Annealing softening by rolling deformation Fig. 3 shows the annealing softening curves of the samples that were aged at 450 °C for 1 h and deformed by 90%, in which it is
evident that an annealing temperature of less than 450 °C has virtually no effect on the hardness. With annealing at 500 °C, the hardness begins to decrease but only by about 6%. Indeed, even with annealing at 700 and 800 °C for 1 h, the microhardnesses of the Pt–0.5Ti alloy was still 3.2 and 2.6 times greater, respectively, than the 50 HV microhardness of Pt. In the Pt–0.3Ti alloy, these values dropped slightly to 2.4 and 2.0 times, respectively, greater than the microhardness of pure Pt. Thus, the Pt–0.5Ti alloy has greater annealing hardness and annealing stability of the considered microalloys. The TEM images in Fig. 4 show that annealing at 500 °C for 1 h partly transforms the microstructure of the deformed (90%) Pt–0.5Ti alloy into a low-angle grain boundary structure, but the dislocation density in the alloy remains high. Because this high dislocation density could effectively prevent recrystallization, it provides an explanation for the slight reduction in the microhardness of the deformed alloy. After annealing at 700 °C for 1 h, the structure is almost fully recrystallized; however, the existence of short dislocations within this crystalline structure helps it retain much of its hardness. Observation by optical microscopy (Fig. 5) revealed that the sample annealed at 800 °C for 1 h was fully recrystallized, which corresponds to the significant reduction in its hardness. 4. Conclusions The microalloying of Pt with small amounts (0.3–0.5 wt%) of Ti has been shown to have a significant solid solution strengthening and process hardening effect, resulting in almost no change in hardness after aging over a very large range of deformation by cold rolling (20–70%). This is due to the fact that the amount of ordered
Fig. 4. The TEM images of rolled (90%) Pt–0.5Ti microalloy after annealing at 500 °C and 700 °C for 1 h.
Fig. 5. Optical images (400) of rolled (90%) Pt–0.5Ti microalloy under different annealing conditions: (a) the partial recrystallized microstructure after annealing at 700 °C for 1 h and (b) the fully recrystallized microstructure after annealing at 800 °C for 1 h.
Y.-m. Guan et al. / Journal of Alloys and Compounds 645 (2015) 34–37
Pt8Ti phase being formed is insufficient to have any significant aging hardening effect. Moreover, the hardnesses of these Pt–Ti microalloys remain relatively high even after recrystallization by annealing, suggesting they have good potential for use as a biomedical electrode material or in jewelry. Acknowledgment The authors would like to thank the National Natural Science Foundation of China (Award No. 51164034) for the financial support provided for this research. References [1] B.K. Woodward, Platinum group metals for permanent implantable electronic devices, in: Niklaus Baltzer, Thierry Copponnex (Eds.), Precious Metals for Biomedical Applications, Woodhead Publishing, 2014, pp. 130–147.
37
[2] Y.T. Ning, Z.F. Yang, F. Wen, Platinum New Application Field, Metallurgical Industry Press of China, Platinum, 2010. [3] N. Sekido, A. Hoshino, M. Fukuzaki, Y. Yamabe-Mitarai, T. Maruko, Steady state creep behavior of zirconia dispersion strengthened platinum alloys, Mater. Sci. Eng. A 528 (2011) 8451–8459. [4] K. Maruyama, H. Yamasaki, T. Hamada, High-temperature creep of GTH (Gottsu-Tsuyoi-Hakkin), Mater. Sci. Eng. A 510–511 (2009) 312–316. [5] M. Besterci, P. Hvizdoš, K. Sülleiová, C. Edtmaier, Processing, microstructure and creep testing of Pt–Y2O3 composites, Mater. Des. 28 (2007) 2540–2543. [6] T. Biggs, S.S. Taylor, E. van der Lingen, The hardening of platinum alloys for potential jewellery application, Platinum Met. Rev. 49 (2005) 2–15. [7] S. Nxumalo, M.P. Nzula, C.I. Lang, Order hardening of Pt8X alloys, Mater. Sci. Eng. A 445–446 (2007) 336–340. [8] M. Carelse, C.I. Lang, Order hardening in platinum 14 at.% copper, Scripta Mater. 54 (2006) 1311–1315. [9] P. Pietrokowsky, Novel ordered phase, Pt8Ti, Nature 206 (1965) 291. [10] K.P. Mabunda, C.I. Lang, The Pt8Zr ordering transformation, J. Alloys Comp. 613 (2014) 375–378. [11] S. Nxumalo, C.I. Lang, Thermodynamic stability of Pt8V, J. Alloys Comp. 425 (2006) 181–184. [12] M.P. Nzula, C.I. Lang, D.J.H. Cockayne, The formation of Pt8Cr in Pt 10 at.% Cr, J. Alloys Comp. 420 (2006) 165–170.