Effect of aging treatment on microstructure and mechanical properties of NiW medium/heavy alloy
Microstructure and mechanical properties of Ni-42W-10Co-1Mo medium/heavy alloy under different aging treatment conditions were studied using optical microscope(OM),scanning electron microscopy(SEM),MT370 electronic universal testing machine and Vickers microhardness tester.The results show that the initial forged microstructure of the alloy is a strip like structure,with obvious fine grains and precipitated phase bands.Within the aging temperature range of 600-900 ℃,as the temperature increases,some grains of the alloy undergo recrystallization,resulting in a more uniform microstructure compared to the forged state,and the precipitated phase σgradually transforms from granular shape in the forged alloy to needle like and block like μ phase(900 ℃).After aging at 700 ℃,the yield strength and tensile strength of the alloy increase from 845.2 and 1187.3 MPa as forged to 924.8 and 1228.8 MPa,respectively,but the plasticity decreases.After aging treatment at higher temperatures(800 and 900 ℃),the strength and plasticity of the alloy show a significant downward trend.The fracture mode of the alloy gradually changes from ductile fracture to mixed fracture with the increase of aging temperature,mainly due to the block and needle like μ phase.
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