| SUN ling-li,HO Hsin-shen,LI Yan-min,ZHANG Er-liang.Surface Roughness Based Characterization of Slip Band for Damage Initiation[J],46(9):240-244 |
| Surface Roughness Based Characterization of Slip Band for Damage Initiation |
| Received:March 17, 2017 Revised:September 20, 2017 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2017.09.038 |
| KeyWord:surface roughness slip bands plastic deformation damage initiation WaspaloyTM superalloy |
| Author | Institution |
| SUN ling-li |
School of Mechanical Engineering, Zhengzhou University, Zhengzhou , China |
| HO Hsin-shen |
School of Mechanical Engineering, Zhengzhou University, Zhengzhou , China |
| LI Yan-min |
School of Mechanical Engineering, Zhengzhou University, Zhengzhou , China |
| ZHANG Er-liang |
School of Mechanical Engineering, Zhengzhou University, Zhengzhou , China |
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| Abstract: |
| To investigate surface roughness resulting from damage initiation of a Ni-base superalloy, and find out a most relevant roughness parameter that can extract the salient features of slip bands. The specimens of WaspaloyTM nickel based superalloy are mechanically polished, then chemically-etched and electro-polished respectively using standard metallographic techniques to obtain two different surface states. The fatigue life is obtained by performing low-cycle fatigue tests. The surface morphology and topographical features of fatigue-induced slip bands are investigated by the transmission electron microscope (TEM) and 3D surface profiler.The most relevant roughness parameter for describing the fatigue-induced surface damage is searched using the variance analysis integrated with the bootstrap method. The surface roughness Sa（Surface arithmetic mean deviation）of electrolytic polishing and chemical etching the is 0.72 nm and 13.3 nm respectively, and the fatigue life of the sample is 800 and 700 after chemical etching and electrochemical polishing. The difference of the increment of the arithmetic mean height (ΔSa=Sa(N)Sa(N0)) is very small for both surface states, and ΔSa is exhibited to be monotonically increasing with the number of cycles (N), the rate at which ΔSa is increased is found to decrease gradually especially when N>100. The electro-polished surface is found to be smoother compared to the chemically-etched one,which offers a slightly greater fatigue crack initiation life. ΔSa does not depend on the surface preparation method and the surface roughness is increasing with ΔSa. Based on a variance analysis integrated with the bootstrap method, the maximum peak height (Sp) is shown to be the most relevant parameter enabling the discrimination of damaged and undamaged grains in slip bands. |
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