Jie-Hao Chen

Study of vibration welding mechanism

Abstract The study on the vertical and horizontal spot vibration welding of Inconel 690 alloy was carried out to observe the dendrite morphologies and estimate the temperature gradient G and growth rate R under different vibration conditions. The purpose is to further understand the mechanism of microstructure changes under vibration. Based on different temperature distributions along vertical and horizontal directions in the centre of a melting pool, it is found that vertical and horizontal vibrations induce the divergence of the nucleates site and grain growth rate then affect the grain morphologies. Vertical vibration welding creates a coarse dendrite structure with sturdy secondary and tertiary dendrite arms, and the X-ray diffraction (XRD) profile of this structure shows a strong (200) peak. Horizontal vibration welding results in grain refinement and a relatively disordered structure, which is reflected by its low XRD intensity. The study shows that vibration affects the weld structure by improving nucleates and changing growth rate.

Microstructure and abrasive wear properties of Fe-Cr-C hardfacing alloy cladding manufactured by Gas Tungsten Arc Welding (GTAW)

A series of Fe-Cr-C hardfacing alloys is deposited by gas tungsten arc welding and subjected to abrasive wear testing. Pure Fe with various amounts of CrC (Cr:C=4:1) powders are mixed as the fillers and used to deposit hardfacing alloys on low carbon steel. Depending on the various CrC additions to the alloy fillers, the claddings mainly contain hypoeutectic, near eutectic, or hypereutectic microstructures of austenite γ-Fe phase and (Cr,Fe)7C3 carbides on hardfacing alloys, respectively. When 30% CrC is added to the filler, the finest microstructure is achieved, which corresponds to the γ-Fe+(Cr,Fe)7C3 eutectic structure. With the addition of 35% and 40% CrC to the fillers, the results show that the cladding consists of the massive primary (Cr,Fe)7C3 as the reinforcing phase and interdendritic γ-Fe+(Cr,Fe)7C3 eutectics as the matrix. The (Cr,Fe)7C3 carbide-reinforced claddings have high hardness and excellent wear resistance under abrasive wear test conditions. Concerning the abrasive wear feature observable on the worn surface, the formation and fraction of massive primary (Cr,Fe)7C3 carbides predominates the wear resistance of hardfacing alloys. Abrasive particles result in continuous plastic grooves when the cladding has primary γ-Fe phase in a hypoeutectic structure.

Sliding wear performance of Fe-, Ni- and Co-based hardfacing alloys for PTA cladding

Abstract Stellite 6, Colmonoy 56, and SKS3 tool steel are typically the materials used as weld hardfacing claddings or as-cast to provide the needed wear resistance to a base material with the required mechanical properties. In this study, a series of Co- and Ni-based hardfacing alloys are successfully fabricated on a substrate of S45C carbon steel using the plasma transferred arc process with Stellite 6 and Colmonoy 56 powders. An Fe-based hardfacing alloy is used on commercial SKS3 tool steel for comparison. The microstructure, hardness and wear resistance of the three materials are investigated systematically. The two claddings and the as-cast SKS3 examined belong to the categories of Co-, Ni- and Fe-based hardfacing, respectively, with hard carbides/borides in their microstructures. The two different claddings are not only tested against SKS3 tool steel but also against each other using the ring-on-disk wear test. After the wear test, the worn surfaces are examined using scanning electron microscopy and energy dispersive spectroscopy to identify the dominant wear mechanisms. The experimental results show adhesive wear is confirmed by metal transfer from a hard surface to a softer one in Stellite 6 against SKS3, and in Colmonoy 56 against the Stellite 6 specimens, while surface deformation testifies to abrasive wear. The transfer layer formed on the surface prevents direct metal-to-metal contact and reduces the wear loss. For Colmonoy 56 against SKS3, adhesion does not occur; instead, Colmonoy 56 causes serious abrasion on SKS3 due to its greater degree of hardness and causes significant wear loss for SKS3.