Study On Forming Process,Microstructures And Properties Of Ni-Cr-B-Si Alloy Parts Prepared By Selective Laser Melting

A wide variety of additive manufacturing technologies have become the focus of the world due to the growing demand for custom parts.Selective Laser Melting?SLM?has been successfully applied in aerospace,medical and other fields due to its short production cycle,no need for molds and fixtures,and no pollution.Mold manufacturing,which has high strength requirements for material,is an important part of industrial production.The SLM process is not limited by the shape and structure of the parts,and the finished products have excellent performance.SLM can be applied to the production of mold inserts with complex structures.This process can reduce waste of material compared with traditional ones,and it is much possible to obtain higher strength parts.Replacing the failed mold inserts with SLM parts can effectively extend the life of the mold.However,due to the limitations of raw material,the use of SLM process in mold manufacturing is still in the research stage.Therefore,it is important to study the manufacturing of higher strength parts by SLM process,which can provide theoretical basis and more possibilities for the application of SLM technology in the field of mold manufacturing and repairing.Ni-Cr-B-Si self-fluxing alloy powder is widely used in mold repairing due to its low melting point and high strength.However,the traditional laser cladding and plasma spraying processes are limited to the repairing of the failed mold surface.SLM is used in this study to print Ni-Cr-B-Si alloy powders with particle size ranging from 21?m to60?m.This provides a new idea for manufacturing mold inserts by SLM process.Firstly,preliminary exploration of the forming process is carried out.The laser energy density is set from 34.72 J/mm³ to 243.06 J/mm³.According to the forming effect of the cubic parts,the laser energy density within 100.00 J/mm³ is more suitable for the formation of the parts,and the laser power is controlled within 200W.Secondly,the laser power and scanning speed are further optimized within a small variation range,and the density of the parts is measured based on the Archimedes principle.The laser energy density is 55.56 J/mm³ at least.The laser power is higher than 100W,and the scanning speed is controlled within 1.2 m/s.Finally,the optimal parameter combination is obtained by three-factor three-level orthogonal test:scanning space h=80?m,laser power P=150 W,scanning speed v=0.6 m/s.The result of the range analysis shows that the scanning space has the most significant effect on the density of the parts.The surface morphology,microstructures and mechanical properties of the alloy parts are analyzed in this study,and the influence of laser energy density on the SLM process is obtained.With the increase of laser energy density,the surface roughness of the parts decreases first and then increases.The part with fine surface quality is obtained when the laser energy density is 78 J/mm³.The value of surface roughness can reach 3.5?m.The wear resistance of the part gets better with the increase of laser energy density.Excessive energy density will cause cracking and warping of the parts.The laser energy density of 80 J/mm³ is more suitable,which can produce a high dense part of 98%.Selective laser melting process has the characteristics of rapid cooling,and this feature makes the alloy parts have fine microstructures.As the laser energy density increases,the crystal growth mechanism of the parts changes from cellular dendrites to equiaxed dendrites.The matrix phases in the part are FeNi₃,?-Ni and Ni₃Si,and the main strengthening phases are M₇C₃,M₂₃C₆ and Cr₂B.During the layer-by-layer superposition process,the formed part is influenced by the heat of the upper layer molten pool,so the hard phases gather in the junction area between two layers continuously.The junction area is easy to crack under the effect of thermal stress.The SLM parts have high microhardness and excellent wear resistance.The average microhardness reaches 848.1 HV_0.5.The wear resistance of the SLM parts is much better than that of the commonly used H13 hot work die steel under the same test conditions.