| Maraging steels are widely used in aerospace,mechanical engineering,precision tools and military applications due to their high strength,high toughness,weldability and excellent machinability after rapid cooling.At the same time,high manufacturing costs and difficulty in ensuring quality stability also limit its application range.Selective Laser Melting(SLM)is suitable for the manufacture of lightweight,complex shaped parts with good mechanical properties and has been used by many scholars for the preparation of maraging steels due to the ease of recovery of the processing powder,which can significantly improve material utilisation and processing efficiency.In this paper,the effect of laser body energy density on the densities,organisation and mechanical properties of moulded parts is investigated under different combinations of laser processes,and the melting and solidification behaviour of powders during SLM moulding under different laser body energy densities is analysed.The effects of heat treatment processes on the structure and mechanical properties of SLM moulded parts are also analysed,as follows:(1)Different combinations of laser process parameters were designed based on the theoretical equation of laser volume energy density.Secondly,different experimental laser process parameters were printed and formed,and then the influence of the microscopic shape of the molten pool on the formed parts was analyzed and verified according to the obtained test results such as density and mechanical properties.It was confirmed that the highest relative density of 99.05%was achieved when the laser energy density was E_v=100 J/mm~3and P,v,h and t were 280 W,933 mm/s,100μm and 30μm respectively.The hardness of the specimens was the highest and the overall tensile properties were the best,with a hardness of 391.4 HV,a tensile strength of 1136.46 MPa and an elongation of up to14.5%.(2)The wear behavior of selected high-performance molded specimens was investigated.The surface shape and element distribution of the wear scar,the coefficient of friction,the area of the longitudinal profile,and the depth and width of the wear scar were analyzed.It was found that the tribological properties of the samples were relatively similar at different laser fluences.The main reason for this phenomenon is that the wear performance is mainly affected by the hardness and strength of the material,and the wear mechanism is mainly adhesive wear and oxidative wear.(3)The SLM molded specimens with the best overall properties(P=280 W、v=933mm/s、h=100μm、t=30μm)were subjected to both direct aging and solution aging heat treatments.It was found that compared with the directly aged samples,the solution aged samples had the best comprehensive mechanical properties,with a hardness of 619.2 HV,a tensile strength of 1974.80 MPa,and an elongation of 7.52%.The wear resistance of different heat-treated samples was judged by the observation and analysis of friction coefficient,wear area and wear morphology.It was found that after solution aging or direct aging,the friction coefficient and wear area decreased significantly,and the wear resistance of the molded samples after aging treatment could be increased by about one time.In the analysis of microstructure and mechanical properties of direct aging samples,it is found that direct aging samples have poor plasticity,high strength and hardness,and their wear mechanisms are mainly abrasive wear and oxidative wear.The solution aging sample has high plasticity while maintaining high hardness and strength,and its wear surface shows a mixture of abrasive wear and oxidative wear,accompanied by adhesive wear and wear. |
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