中文摘要：

在Ar气和空气环境中激光立体成形了Inconel 718镍基高温合金坯.显微组织观察、拉伸性能和高周疲劳性能测试结果表明：Ar气和空气环境中成形合金的沉积态和热处理态组织基本相同,沉积态组织为沿沉积方向连续生长的粗大柱状枝晶,组织细密,均匀;热处理后发生再结晶,柱状晶转变为等轴晶;2种气氛下成形件热处理后的静载拉伸性能满足锻件标准,空气环境中成形试样的拉伸强度略高于Ar气环境中成形的试样,但是前者的塑性略低;前者的疲劳性能比后者约低30%,这主要是由于空气中成形的试样中存在较多的氧化物夹杂和显微气孔等缺陷;二者的疲劳性能均低于锻件标准,主要原因是试样中存在氧化物夹杂、显微气孔等冶金缺陷以及热处理后的晶粒尺寸较大.

英文摘要：

Due to the rapid melting and solidification in laser molten pool,the laser solid forming （LSF） samples have generally much finer microstructure than that of the conventional cast,and are also free of macrosegregation.To date,more and more researchers have reported the application of LSF technology in the forming of superalloy,which contains some easily segregated elements such as Nb,Ti and Al.To prevent the molten pool from oxidation,the LSF process usually should be performed within a protective atmosphere.But in practice,the forming of oxidation-resistant metals are always performed in the air atmosphere and only the molten pool is protected by noble gas. Therefore,it is important to investigate the microstructures and properties of LSF materials prepared in the air and noble gas.In the present study,the microstructures,tensile properties and high cycle fatigue properties of LSF Inconel 718 alloy samples prepared in the air and argon atmospheres were investigated.It is indicated that the microstructures in as-deposited and heat-treated LSF Inconel 718 alloy samples prepared in both atmospheres are similar.The as-deposited microstructure consists of columnar dendrites grew epitaxially along the deposition direction from the substrate,and changes to the equiaxed grains after solution heat treatment due to the recrystallization.The tensile properties of the two kinds of the samples after heat treatment reached the standard for wrought Inconel 718 alloy. The tensile strength of the sample prepared in air is slightly higher than that of the sample prepared in the argon atmosphere,and the high cycle fatigue lifetime of the latter is 30%higher than that of the former,which is related to the fewer defects such as micro pores and small size oxide inclusions existed in the former.The lower high cycle fatigue property of LSF Inconel 718 alloy than that of wrought Inconel 718 alloy is attributed to the metallurgical defects and the coarsening and uneven distribution of the recrystallized grains.