Abstract
A high-power direct diode laser (HPDDL) having a rectangular beam with a top-hat intensity distribution was used to produce surface-hardened layers on a ferrous alloy. The thermal conditions in the hardened zone were estimated by using numerical simulations and infrared (IR) thermography and then referred to the thickness and microstructure of the hardened layers. The microstructural characteristics of the hardened layers were investigated using optical, scanning electron and transmission electron microscopy together with X-ray diffraction. It was found that the major factor that controls the thickness of the hardened layer is laser power density, which determines the optimal range of the traverse speed, and in consequence the temperature distribution in the hardened zone. The increase in the cooling rate led to the suppression of the martensitic transformation and a decrease in the hardened layer hardness. The precipitation of the nanometric plate-like and spherical cementite was observed throughout the hardened layer.
Highlights
Laser surface treatment methods have been intensively employed for the past three decades for the enhancement of surface properties of different cast iron grades [1–13].Much research has been devoted to improving the tribological properties of cast irons via a laser surface transformation hardening (LSTH) process [10–12,14–18]
[27,28].hardness, On the other lower traverse speeds, ensuring lower values of the cooling rate, are beneficial in produchand, to avoid surface melting with increasing power density, the elevation of traverse ing more wear-resistant layers theboth other to avoid surface melting with speed is required
The laser source used was a high-power direct diode laser having a rectangular beam with a top-hat intensity distribution
Summary
Laser surface treatment methods have been intensively employed for the past three decades for the enhancement of surface properties of different cast iron grades [1–13]. Much research has been devoted to improving the tribological properties of cast irons via a laser surface transformation hardening (LSTH) process [10–12,14–18]. In contrast to conventional surface hardening processes such as induction and flame hardening, LSTH ensures excellent surface finish and very low distortion of the workpiece. In many cases, this eliminates any need for post-treatment finishing [19]. There has been significant interest in the application of LSTH to increase the tribological performance of ductile cast irons (DCI) in both the as-cast condition and after austempering heat treatment [14–17]
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