Electron Backscatter Diffraction (EBSD) analysis of laser-cladded AISI 420 martensitic stainless steel

Abstract

Laser cladding is a laser-based additive manufacturing (AM) process that is currently being used to coat part of a substrate or to produce a three-dimensional object in layer by layer following a computer-controlled instruction. In this study, laser-cladded AISI 420 martensitic stainless steel was characterized using the Electron Backscatter Diffraction (EBSD) technique to analyze the substructure of martensite in the selected zones such as the bead zone (BZ), the dilution zone (DZ), and the interface with the heat affected zone (HAZ) of the bead. The EBSD prior austenite grain (PAG) maps and inverse pole figure (IPF) revealed planer and columnar grains at the interface and within the adjacent dilution zone, while equiaxed and a combination of both columnar and equiaxed grains were observed in the center of the bead and dilution zone. The Grain Orientation Spread (GOS) and grain average Image Quality (IQ) techniques were used to quantify the grain misorientation and residual strain/stress in those selected zones. The EBSD analysis with the GOS and IQ values confirmed deformation and strain in the crystal lattice structure of those respective zones. The GOS approach revealed that most of the grains at the BZ and HAZ were highly strained and 26–59% fraction of the grains was at a high angle of GOS (3°–5°) indicating the availability of highly deformed grains in both regions. The IQ value was compared and correlated with the experimental values of residual stresses (RS) measured by XRD methods to understand residual strain distribution in those zones. It was revealed that the IQ value is inversely proportional to the RS value found in an earlier study. This EBSD parameter is expected to be used as an alternative method of analyzing RS distribution in the laser-cladded coating.