Influence of processing parameters on the properties of AISI 4340 steel coated with TiC powder fabricated by tungsten inert gas arc melting

Abstract

The incorporation of TiC through surface melting at high energy input was found to produce a thin layer of hard coated material on the surface of the substrate beneficial for wear resistant. This work involved the cheap TIG melting technique to melt the hard TiC particulates on the AISI 4340 low alloy steel substrate material rather than the expensive laser or electron beam method. The experimental work involving three phases were initiated by producing single melt layers at different processing conditions in order to identify the sample that exhibits high hardness values that is crack free associated with densed population of TiC microstructures. The characterization of the single layer and multipass layers were affected by the microstructural features and surface topography investigated using optical microscope (OM), scanning electron microscope (SEM) and X-Ray diffraction (XRD) while the microhardness values were conducted using Vicker microhardness machine. Under the first phase, the calculated energy used was varied from the lowest at 1008 J/mm to 2640 J/mm while the powder content was in the range of 0.4 mg/mm2 to 2 mg/mm2. The shielding argon gas was from 10 l/min to 30 l/min and the measured working distance was at 0.5 mm to 1.5 mm. The optimum processing condition for this single layer at 1344 J/mm with 1 mg/mm2 powder content produced crack free sample with hardness value up to 4 times than the substrate material. The second stage involved melting for multipass layers using the single layer optimum processing condition to be overlapped at the 50% of offset distance. The preheating effect from re-melting of the previous layers at this stage dissolved more of TiC particulates for homogeneity of re-precipitated TiC microstructures across the melt track. With the multipass layers, the microhardness ranges from 600 HV to 1000 HV which is over two times than the substrate. In the third stage, investigation of the wear behavior was conducted at the room temperature of 20oC under the dry sliding wear test using alumina ball as the counterpart. The improvement of hardness by the coated layer up to 2.3 times than the substrate exhibited 13 times lesser of wear rate than the uncoated sample that was seen to endure wear severance dominated by deformation. The persistency of oxidative, adhesive and abrasive wear mechanism appeared on the samples resulted difference of surface morphologies that had much influenced the value of friction coefficients. The research may provide additional knowledge and information to produce hard coated layer for the suitability of technology application in industries like, automotive, aerospace and oil and gas.