采用无坩埚感应熔炼超声气体雾化法制备Ti-5Al-2.5Sn ELI预合金粉末, 并对预合金粉末进行表征. 研究了热等静压参数对Ti-5Al-2.5Sn ELI粉末合金显微组织和力学性能的影响. 结果表明, 热等静压温度和压力的升高有助于提升粉末合金的致密度, 当粉末合金的致密度大于99.5%时, 粉末合金的力学性能可以达到锻造合金的水平. 综合考虑粉末合金的致密度、显微组织和力学性能, Ti-5Al-2.5Sn ELI预合金粉末优选的热等静压工艺成型窗口为温度890~940 ℃, 压力120 MPa以上, 保温保压3 h. 包套对热等静压压力有屏蔽作用, 设计不当会降低粉末压坯的致密度. 通过优化包套设计、热等静压参数和工艺途径可以有效抑制包套的屏蔽作用, 提升粉末合金的致密度.
Near-net-shape forming through powder metallurgy (PM) route is a cost-efficient approach to produce the hard-to-machining materials such as titanium alloys. Hot isostatic pressing (HIPing) is a common technique to fabricate PM titanium alloys and components. Prealloyed powder metallurgy through HIPing is considered as upgrade of precision casting for titanium alloys. Ti-5Al-2.5Sn ELI (extra-low interstitial) is a typical α-Ti alloy, which is widely used at cryogenic temperature. In this work, the Ti-5Al-2.5Sn ELI prealloyed powder was produced by electrode induction melting gas atomization. Characterization of the prealloyed powder was carried out to understand the following HIPing process. The influence of HIPing parameters on microstructure and mechanical properties of Ti-5Al-2.5Sn ELI powder compact was studied. The results show that the relative density of powder compact increases with the increasing of HIPing temperature and pressure. The mechanical properties of powder compact can achieve those of wrought materials, when the relative density is more than 99.5%. To balance the relative density, microstructure and mechanical properties of the powder compacts, the optimized HIPing parameters for Ti-5Al-2.5Sn ELI powder are temperature in the range of 890~940 oC, pressure above 120 MPa and holding for 3 h. The shielding effect of capsule will hinder the powder densification during HIPing process, which will likely cause non-uniform densification and degrade the relative density of powder compact. However, the shield effect can be weakened through proper tooling design and optimization of the HIPing procedure.
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