Structure control and densification of sintered titanium alloys

烧结钛合金的结构控制和致密化

• 批准号: 08650851
• 负责人: TAKAKI Setsuo
• 金额: $ 1.15万
• 依托单位: KYUSHU UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1996
• 资助国家: 日本
• 起止时间: 1996 至 1997
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08650851/
• 关键词: Powder metallurgy; Titanium alloy; Structure control; Mechanical property; Density; Pore; Forging; Superplasticity; 粉末治金

Ti-4mass%Cr alloy, which was developed in this study, can easily be produced from commercial powders of titanium and chromium through the usual powder metallurgy process ; mixing of powders, molding of the mixed powder and then sintering in vacuum. Since this alloy has BCC strructure (beta-phase) at elevated temperature above 900C which is excellent in difusivity of elements, the sintering treatment of 1250C-1hr results in 1) homogenization of chemical composition and 2) increasing of density of sintered materials to 92% in relative density. The alloy has good mechanical properties under the as-sintered condition, but due to the retained pores, it is also cleared that there are some disadvantages in fracture toughness and fatigue strength. To get over these disadvantages, the density of sintered materials should be increased to 99% or over in relative density. The nature that beta-phase is enough soft at elevated temperature makes easy forming and complete densification of sintered materials possible. Pores retained in sintered materials are closed ones and the innersurface of pores is clean, hence they can fully disappear during deformation for forming without inner-oxidation of pores. In addition, it was also found that this alloy undergoes superplastic deformation at around 700C,when sintered materials were subjected to an appropriate treatment in advance : Sintered materials was once water-quenched from beta-phase region to obtain martensitic structue and then sufficiently deformed at 700C to change the martensitic structure to fine-equiaxd grains. Superplastic deformation is very helpful for developing the rnrformance in formability of this alloy.

本研究开发的Ti-4mass%Cr合金，可以通过常规的粉末冶金工艺从工业钛和铬粉末中轻松制备；混合粉末，将混合粉末成型，然后在真空中烧结。由于该合金在900℃以上高温下具有BCC组织（β相），元素的扩散性能优异，1250C-1hr的烧结处理导致1)化学成分均匀化，2)烧结材料的相对密度提高到92%。该合金在烧结状态下具有良好的力学性能，但由于气孔的残留，在断裂韧性和疲劳强度方面也存在一定的缺点。为了克服这些缺点，烧结材料的相对密度应提高到99%或以上。β相在高温下足够软的性质使得烧结材料易于成形和完全致密化成为可能。烧结材料中保留的孔隙是封闭的，孔隙内表面清洁，因此在变形成形过程中可以完全消失，不会引起孔隙的内氧化。此外，还发现该合金在700C左右发生超塑性变形，此时对烧结材料进行适当的预处理：烧结材料先从β相区水淬，得到马氏体组织，然后在700C进行充分变形，使马氏体组织转变为细等轴晶粒。超塑性变形有助于提高该合金的成形性能。