J. Mater. Sci. Technol. ›› 2022, Vol. 125: 171-181.DOI: 10.1016/j.jmst.2022.01.036

• Research Article • Previous Articles     Next Articles

Additive manufacturing of a Co-Cr-W alloy by selective laser melting: In-situ oxidation, precipitation and the corresponding strengthening effects

Kefeng Lia,b, Zhi Wangc, Kaikai Songd, Khashayar Khanlaria,b, Xu-Sheng Yange,f, Qi Shia,b, Xin Liua,b,*(), Xinhua Maoa,b   

  1. aInstitute of New Materials, Guangdong Academy of Sciences, Guangzhou 510650, China
    bNational Engineering Research Center of Powder Metallurgy of Titanium and Rare Metals, Guangzhou 510650, China
    cGuangdong Key Laboratory for Advanced Metallic Materials Processing, South China University of Technology, Guangzhou 510641, China
    dSchool of Mechanical, Electrical and Information Engineering, Shandong University, Weihai 264209, China
    eAdvanced Manufacturing Technology Research Center, Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China
    fHong Kong Polytechnic University Shenzhen Research Institute, Shenzhen 518000, China
  • Received:2021-08-30 Revised:2021-12-28 Accepted:2022-01-09 Published:2022-04-16 Online:2022-04-16
  • Contact: Xin Liu
  • About author:* Institute of New Materials, Guangdong Academy of Sciences, Guangzhou 510650, China. E-mail address: liuxin@gdinm.com (X. Liu).

Abstract:

Additive manufacturing exhibits great potentials for the fabrication of novel materials due to its unique non-equilibrium solidification and heating process. In this work, a novel nano-oxides dispersion strengthened Co28Cr9W1.5Si (wt.%) alloy, fabricated by laser powder bed fusion (LPBF), was comprehensively investigated. During the layer-by-layer featured process, in-situ formation of Si rich, amorphous, nano-oxide inclusions was observed, whose formation is ascribed to the high affinity of Si to oxygen. Meanwhile, distinctive body-centered cubic (BCC) Co5Cr3Si2 nano-precipitates with an 8-fold symmetry were also confirmed to appear. The precipitates, rarely reported in previous studied Co-Cr alloys, were found to tightly bond with the in-situ oxidization. Furthermore, the morphologies, the size distributions as well as the microstructure of the interface between the matrix and the inclusions were investigated in detail and their influence on the tensile deformation was also clarified. The existence of transition boundaries between these inclusions and the matrix strongly blocked the movement of dislocations, thereby increasing the strength of the alloy. It was understood that when the plastic deformation proceeds, the fracture occurs in the vicinity of the oxide inclusions where dislocations accumulate. A quantitative analysis of the strengthening mechanism was also established, in which an additional important contribution to strength (∼ 169 MPa) caused by the effects of in-situ formed oxide inclusions was calculated.

Key words: Co-Cr-W-Si alloy, Selective laser melting, Oxide inclusion, Precipitation, Strengthening mechanisms