A critical evaluation of the microstructural gradient along the build direction in electron beam melted Ti-6Al-4V alloy

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:744

Article

Sharma, H.¹  Parfitt, D.¹  Syed, A. K.¹  Wimpenny, D.²  Muzangaza, E.²  Baxter, G.³  Chen, B.^1,4 

[1] Coventry Univ, Fac Engn Environm & Comp, Coventry CV1 5FB, W Midlands, England

[2] Mfg Technol Ctr Ltd, Pilot Way,Ansty Pk, Coventry CV7 9JU, W Midlands, England

[3] Rolls Royce PLC, Derby DE24 8BJ, England

[4] Coventry Univ, Inst Adv Mfg & Engn, Beresford Ave, Coventry CV6 5LZ, W Midlands, England

关键词: Electron beam melting;    Additive manufacturing;    Graded microstructure;    Mechanical property;    Titanium;   

DOI  :  10.1016/j.msea.2018.12.016

来源: Elsevier

【 摘 要 】

It is generally recognised that electron beam melted (EBM) Ti-6Al-4V alloys exhibit a microstructural gradient along the build direction, but there have been some inconsistent experimental observations and debate as to the origin and magnitude of this effect. Here we present an unambiguous evaluation of this microstructural gradient and associated mechanical property along the EBM build direction on purpose-built round bar RB samples with build height of 380 torn and rectangular plate RP samples with build height of 120 mm. Columnar prior beta grain width was found to increase (from 86 +/- 38 to 154 +/- 56 mu m in RB and from 79 +/- 34 to 122 +/- 56 mu m in RP samples) with the build height and the similar increase was also observed for a lath width (from 0.58 +/- 24 to 0.87 +/- 33 mu m in RB and from 1.50 +/- 45 to 1.80 +/- 49 mu m in RP samples). These observations can be attributed to the thermal gradient in the powder bed that produced a cooling rate gradient along the build height. The measured a lath width variation along the build height followed a log-normal distribution. The graded microstructure resulted in a decrease in micro-hardness which correlated very well with the mean a lath width by following a Hall-Petch relation.

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