Microstructure and Hardness of Electron Beam Selective Melting Formed TC4 Titanium Alloy
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摘要: 采用电子束选区熔化成形技术制备不同尺寸(ϕ8 mm×25 mm,ϕ25 mm×8 mm)TC4合金试样,研究了2种试样在粉末堆积方向的显微组织及硬度变化。结果表明:尺寸ϕ8 mm×25 mm试样的显微组织主要由原始β柱状晶界处的针状α集束组织和晶内针状α相互相交错形成的网篮状魏氏组织组成,原始β柱状晶主轴平行于堆积方向并且贯穿各熔合层,残余β相弥散分布在α相基体中;尺寸ϕ25 mm×8 mm试样顶部组织由针状α'相组成,中部组织中α'相受热分解为α相和β相,α相宽度较大,底部组织中条状α相贯穿原始β晶粒形成集束,残余β相在α相基体中呈连续网状分布。具有较大长宽比针状α相或α'相部位的显微硬度比具有较小长宽比条状和片状α相或α'相的硬度高。Abstract: The TC4 alloy samples with different dimension(ϕ8 mm×25 mm, ϕ25 mm×8 mm) were fabricated by electron beam selective melting forming technique. The evolution of microstructure and hardness along the powder deposition direction was studied. The results show that the microstructure of the sample with dimension of ϕ8 mm×25 mm was composed of acicular α clusters at prior β columnar grain boundaries and net-basket-shaped widmanstatten structures formed by interlaced acicular α phase in grains. The axis of prior β columnar grains was parallel to the direction of powder deposition and grew through every deposition layer. The residual β phase dispersed among α phase matrix. The top microstructure of the sample with dimension of ϕ25 mm×8 mm consisted of acicular α' phases. The acicular α' phase in the middle microstructure was decomposed into α phase and β phase, and the width of α phase was relatively large. The strip α phase in the bottom microstucture grew through prior β grains to form clusters. The residual β phase dispersed in the continuous network among α phase matrix. The microhardness of the part with acicular α or α' phase of large length-width ratios was higher than that with strip and lamellar α or α' phase of small length-width ratios.
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Keywords:
- electron beam selective melting /
- TC4 titanium alloy /
- microstructure /
- microhardness
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