Microstructural effects on properties of as-fabricated Inconel 625 with direct energy deposition process

¹ Department of Mechanical and Mechatronics, Tshwane University of Technology, South Africa, Staatsartillerie Road, Pretoria West, Pretoria, 0183
² Department of Mechanical and Mechatronics, Tshwane University of Technology, South Africa, Staatsartillerie Road, Pretoria West, Pretoria, 0183
³ Department of Mechanical and Mechatronics, Tshwane University of Technology, South Africa, Staatsartillerie Road, Pretoria West, Pretoria, 0183
⁴ CSIR, Photonics Centre, Laser Enabled Manufacturing Group, Pretoria Campus, 0001, South Africa

^* Corresponding author: twjbooysen@gmail.com

Abstract

Three-dimensional printing (3D), also known as metal additive manufacturing (MAM), fabricates parts or components from different feedstocks: wires, powders or sheets. This process differs from traditional manufacturing techniques such as casting, moulding, or subtracting existing materials. In the development and improvement or fabrication of new materials for higher strength and various applications, the type or character of a material is very important as this will ascertain the strength of the finished product. Direct energy technology can be used to fabricate and repair parts or components with the following two fabrication methods: laser wire-directed energy deposition (LW-DED) or laser powder-directed energy deposition (LP-DED). In this research, laser powder-directed energy deposition (LP-DED), a MAM process method, was employed to fabricate Inconel 625. The LP-DED process uses a laser as a heat source and rapidly melts metallic powders of different chemical compositions to fabricate complex structures, which is an innovative three-dimensional material processing technology. The as-fabricated (AF) sample specimens were investigated to determine the microstructural development, microhardness and sample defects. The microstructural features were analysed using two experimental surface microscopy methods: light optical microscopy (LOM) and scanning electron microscopy (SEM). The morphological grain structure within the samples was predominantly cellular, columnar and columnar-dendritic. Energy dispersive X-ray (EDX) and X-ray diffraction (XRD) analysis were performed to determine the chemical composition and crystallographic structures of virgin gas atomisation (GA) powder and as-fabricated sample. The XRD peaks in samples composed of face-centred-cubic (FCC) γ-nickel phase. The material microhardness was studied by performing Rockwell hardness test (HRB) with a fluctuated trend averaging 98.9 – 101.6 HRB. The relationship between processing, microstructure, grain structure and material hardness was systematically summarised and established. The study concluded with research suggestions on LP-DED of Inconel 625.