Investigation On Microstructure And Properties Of Laser Cladding TiC-Fe₃Al-Ni Coatings On High-Speed Steel Surface

High-speed steel materials are mainly used to manufacture complex shapes and forming tools,but there are serious wear,stress corrosion and fatigue failure phenomena in engineering applications.Among them,wear is the main factor causing component failure and severely reducing tool cutting performance.Make it limited in engineering applications.In order to improve the surface wear resistance of high-speed steel and to achieve the purpose of repairing damaged high-speed steel parts.In this paper,the laser cladding technology is used,the TiC-Fe₃Al-Ni composite powder is selected as the cladding material,and the KJG-1YAG-400A laser welding machine is used to prepare the surface of W18Cr4V high speed steel by optimizing the laser process parameters.A composite cladded layer has good molding quality,high hardness and high wear resistance.In order to improve the comprehensive performance of high-speed steel surface,prolong the service life of high-speed steel parts in engineering applications,and provide theoretical basis and experimental guidance for optimizing laser cladding process parameters.The main findings are as follows:?1?In this paper,a single factor experiment was designed to investigate the influence of laser process parameters?including laser current,pulse width,pulse frequency,defocusing distance,and scanning speed?on the surface morphology and melting width of the cladding layer.The melted width of the layer will be increased with the laser current,and pulse width and pulse frequency growing up.And the width decreases with the increase of laser scanning speed.As the defocusing distance increases,the melted width will be broaden after decrement.?2?The thickness of the preset layer is 1 mm.Through the orthogonal test,the surface roughness,microhardness,cross-sectional porosity and crack rate of the cladding layer are comprehensively scored.and the optimal laser process parameters are laser current 370 A,pulse width 7 ms,pulse frequency 4 Hz,defocusing distance 4 mm,Scanning speed 3 mm/s.?3?Scanning electron microscopy?SEM?,energy spectrum analyzer?EDS?,X-ray diffractometer?XRD?and micro-hardness tester were used to weld different laser scanning speeds and different Ni content.The physico-chemical properties,such as the macroscopic structures,localized microstructures,element distributions as well as the phase and micro-hardness distributions,had been detected in the cladded layer sections.The results showed that the cladded layer with a good quality and compact structure had been obtained under the optimized laser process parameters.The cladded layer is mainly composed of TiC,TiWC₂,C5Ti₄W,AlNi,AlV₃,TiO and FeO phases,and element diffusions occur at the transition zone between two substrates and form an excellent metallurgical combination.As the laser scanning speed increases,the phase composition in the cladding layer is hardly changed,and the dense layer is generated with a gradually thickened layer.On the part of TiC morphology of the hard phase,a transformation from dendritic to short rod and granular has been realized in the laser cladding process.The average micro-hardness of the cladded layer gradually increased and the maximum value can be up to 2674 HV,about 3.2 times the substrate.?4?By studying the effect of adding different Ni content on the cladding layer,the results show that there are a lot of cracks and pores inside the cladding layer without adding Ni powder,the internal structure is uneven,and the structure of many regions is loose;by adding 0.5 wt%Ni The powder can effectively reduce the internal crack and porosity of the cladding layer,and the micro-hardness decreases little.The inside of the cladding layer with 1 wt%and1.5 wt%Ni powder is basically free of cracks and pores,but the micro-hardness decreases greatly.?5?According to the tribological results,the average friction factor of the cladding layer decreases first and then increases with the increase of laser scanning speed.The layer produced at a scanning speed of 4 mm/s has the smallest friction coefficient,it is about 0.25.The frictional factors of the cladded layer with scanning speed greater than 2 mm/s are smaller than the matrix.And the worn surface has slight fluctuation.The wear mechanism of the cladded layer is gradually changed from the wear dominated by adhesive wear and abrasive wear to the peeling wear.And the wear resistance of cladded layer fabricated at the condition of laser scanning speed of 5 mm/s has been well above 16 times than the matrix.The main wear mechanism of the cladded layer without Ni powder is stripping wear.There are many cracks on the worn surface as well as brittle sheddings around the crack.Additionally,the wear loss is relatively large.The main wear mechanism of the cladding layer with 0.5 wt%Ni powder is also stripping wear.but the worn surface has few cracks and the wear loss is the smallest on.As for cladded layer with 1 wt%and 1.5 wt%Ni powder,adhesive wear and abrasive wear are found in sliding test.And the critical wear had been detected on the worn surface.