Study On Structure And Mechanical Properties Of Pt-Ti-X(Zr、Hf)Microalloy

Platinum has excellent properties of high melting points and corrosion resistance, as well as notable anti-oxidation and catalytic activity; especially it cannot be replaced by other cheaper materials. So that platinum metals are widely used in various industries. However, the poor strength of pure Pt at room temperature severely limits their applications. Therefore, we expect to improve the mechanical properties of platinum microalloy at room temperature by alloying with micro-mount of Ti, Zr, Hf elements, and thermomechanical process in this work.In this paper, three components microalloy were mixed and melted on a water-cooled copper hearth using a vacuum/argon arc melter. The nominal composition of three components microalloy is:Pt-0.7Ti, Pt-0.5Ti-0.2Zr and Pt-0.5Ti-0.2Hf (wt.%). The effects of cold rolling, solid solution, aging and annealing treatment on microalloys are investigated in this study. The microstructures of the microalloy for cold-rolled and heat treatment (solid-solution, aging) are observed and analyzed by OM, TEM, XRD. The mechanical properties of the alloy are evaluated by Vickers microhardness test and tensile test. The results show that:(1) Micro-amount of Ti, Zr, Hf are effective elements for solid-solution strengthening of Pt. The highest microhardness is147HVo.2for Pt-0.5Ti-0.2Zr after solid-solution treatment. The microhardness values of Pt-0.7Ti and Pt-0.5Ti-0.2Hf is118HV0.2and99HVo.2, respectively. These have being2.5,2and1.7times than as-casted pure Pt, respectively. In the case of that total alloy composition is0.7wt.%, the strengthening effect of solid solution Pt with the Ti and Zr element is the most prominent, a single element Ti stronger than the binary elements Ti and Hf.(2)Aging was conducted at different conditions, but the effect of aging hardening in Pt-Ti-X (Zr, Hf) microalloy is not obvious.(3)The Pt-Ti-X (Zr、Hf) microalloys endured multi-pass continuous rolling to a maximum deformation of97%at room temperature, show excellent processing performance, and outstanding work hardening effect. Microhardness of the S+CR and AG+CR for Pt-0.7Ti compare with the solid solution, aging state increased by81%and79%,respectiviely.Another,Pt-0.5Ti-0.2Zr increased by67%and60%, respectively, Pt-0.5Ti-0.2Hf increased129%and117%, respectively. The AG+CR Pt-0.5Ti-0.2Zr microalloy has the highest microhardness253HVo.2.(4)The microhardness and microstructures by large rolling deformation samples are almost not changed after an annealing below500℃for1h. When the annealing temperature elevated to700℃, the micohardness values of the microalloys decrease by20%-25%, and recrystallization is not complete. Annealed at800℃for1h, the microhardness still2.5to4.2times than that of pure Pt (38HV0.2), the AG+CR three microalloys and S+CR Pt-0.7Ti are fully recrystallized, and grains have grown, but the S+CR Pt-0.5Ti-0.2Zr, Pt-0.5Ti-0.2Hf alloys have not completed fully recrystallization. The recrystallization temperature rose200℃at least compared with pure Pt.(5)Tensile strength of the three components microalloys has been greatly improved. The maximum tensile strength up to740MPa (AG+CR Pt-0.5Ti-0.2Zr), it is about2.2times that of pure Pt. After annealed at800℃for1h, tensile strength of the microalloys still2.4to3.4times than pure Pt(119MPa),the Pt-0.5Ti-0.2Zr has the highest tensile strength(415MPa), while Pt-0.5Ti-0.2Hf possesses the maximum elongation up to29%.In summary, the mechanical properties of platinum based microalloy are significantly improved by micro-alloying; solid-solution treatment and work harden. In addition, trace amounts of alloying elements delay the softening annealing significantly, and make annealed micro-alloys with good mechanical properties. This shows a great potential value to widen the application of platinum in the practice.