Effect of aging process on surface cracking and hardness of NiCrWCo springs
NiCrWCo alloy is a key material in aero-engine,and its moulded springs form a large number of cracks on the surface due to its high alloying and complex moulding process.The cracks and hardness of the alloy are analysed from the cross-section,the microstructure and elemental distribution of the material are analysed by SEM&EDS,and the microhardness is used to evaluate the effect of aging process on the mechanical properties of the cross-sec-tion.The results show that there exists a layer of precipitate free zone(PFZ)on the surface of the alloy,and under the effect of inclusions,the PFZ in the surface layer of the alloy cracks before winding,and then after the winding process,the cracks continue to expand internally.Both aging processes enhance the hardness of the material,with the aging process Ⅱ providing the greatest enhancement(659.3 HV).After the aging process,a Cr2O3-Al2O3 double-layer oxide film of about 4 pm is formed on the surface of the alloy,but the oxide film is easily detached due to the presence of cracks and insufficient Al content.The PFZ hardness at the edges is lower than the overall aver-age hardness of the alloy,and the hardness distribution of the alloy cross-section is characterised by irregularities due to inclusions and inhomogeneous deformations in the drawing process.
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