Characterization of weldability, microstructure, and corrosion resistance of dissimilar welded joint between Mo 2 FeB 2
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The joint of dissimilar metals between Mo2FeB2-based cermets and 316L stainless steel was welded by gas tungsten arc welding with no fillers. The weldability was investigated by plate rigid restraint cracking test and transverse rupture strength was measured by the three-point bending test. Microstructure of the weld joint was studied with scanning electron microscope, energy-dispersive spectrometer, X-ray diffractometer and differential scanning calorimeter, etc. Corrosion behavior was investigated by the potentiodynamic polarization test. Results revealed that weld solidification cracking susceptibility existed in the fusion zone. Coarse irregular complex ternary boride phase (M3B2) and hypoeutectic microstructure were formed in weld metal (WM). In heat affected zone (HAZ), a small number of M3B2 grains dissolved into the c-Fe based binder, with growth and coalescence of the remaining M3B2 grains. Microhardness of HAZ increased slightly and WM presented the highest microhardness in the whole joint. Besides, potentiodynamic polarization test showed that WM had a better corrosion resistance than Mo2FeB2-based cermets, which can be attributed to the higher Cr content and relatively homogenous Mo distribution.
I. INTRODUCTION
Mo2FeB2 ternary boride based cermets have been widely applied to wear resistance parts such as injection molding machine parts, hot copper extruding dies, and tools making due to their superior intrinsic properties, for example, high hardness, high melting point, and excellent corrosion and oxidation resistance.1–3 In the past few years, the effects of preparation techniques3 and additional elements such as Cr,4 Ni,5 Mn6 and V7 on the properties of Mo2FeB2-based cermets have been well studied. In particular, Takagi3 proposed the criteria for the production of boride base cermets, that is, selecting a suitable boride which coexists with the metal matrix for the formation of a two phase structure, avoiding the formation of a brittle third phase, preventing grain growth during sintering and forming a liquid phase between the boride and metal matrix to obtain full densification of a sintered product. Complying with these criteria, the technique called “reaction boronizing sintering” was exploited, through which the cemented boride with desired microstructure and excellent mechanical properties can be obtained. Inspired by the perfect performance of Mo2FeB2 ternary boride based cermets, several researchers have Contributing Editor: Yang-T. Cheng a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.311 J. Mater. Res., Vol. 30, No. 23, Dec 14, 2015
made efforts to investigate the preparation of Mo2FeB2based cermets coatings.8–10 Surface engineering techniques such as reactive thermal spraying and laser cladding have been used to fabricate the Mo2FeB2-based cermets coatings, which have significantly improved the hardness and wear resistance of the substrate. However, few studies have focused on the joining of Mo2FeB2-based cermets, especially the joining of Mo2FeB2-
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