基于激光复合再制造技术的H13钢粉末修复45钢的组织演变及耐磨性增强

Microstructure Evolution and Wear Resistance Enhancement of H13 Steel Powder Repaired 45 Steel Using Laser Composite Remanufacturing

激光定向能量沉积(LDED)是受损大型关键构件几何特征修复和性能强化的典型修复技术,但其目前仍面临残余应力、孔洞和裂纹等问题。激光冲击强化(LSP)为解决以上问题提供了新思路。笔者以H13钢粉作为待沉积粉末,采用LDED技术对受损的45钢基体进行修复;然后利用LSP后处理强化LDED修复层,以解决传统LDED修复材料的质量问题。结果表明:随着LDED激光功率增大,H13钢修复层的晶粒逐渐细化,渗碳体溶解,耐磨性提升;LSP后处理会使修复层近表层的晶粒明显细化,显著降低LDED修复试样的摩擦因数,进一步提升其耐磨性。最后,笔者系统揭示了LDED+LSP激光复合再制造工艺诱导的微观组织演化(晶粒细化和渗碳体溶解)及其增强修复层耐磨性的机制。

Objective AISI 1045 steel(45 steel)has good plasticity,ductility,and excellent mechanical properties and is widely used in automotive manufacturing.However,the surface of the material can be damaged by friction,leading to a deterioration in the performance of components in contact with moving parts.Further,damage caused by corrosion and abrasion accelerates the expansion of cracks and risks fracture.Partial remanufacturing is an effective way to reservice damaged parts,maximizing the residual value of the material.Laser additive manufacturing is considered the most promising remanufacturing technology for rebuilding the geometric features of damaged parts and restoring their mechanical properties;however,it faces problems concerning material properties.In this study,an innovative combination of laser directed energy deposition(LDED)and laser shock processing(LSP)processes is proposed for the remanufacture of damaged 45 steel,utilizing the respective advantages of each process.Methods Experiments were conducted on 45 steel,whose chemical composition is displayed in Table 1.H13 tool-steel powder was used as the laser deposition powder for the experiments,and its chemical composition is displayed in Table 2.The laser composite remanufacturing process was realized using LDED and LSP equipment,and the specimens were fabricated according to LDED and LSP experimental parameters:a 2 mm thick layer was deposited on the substrate using LDED,milled to a smooth surface,and treated with LSP.Finally,the specimens were cleaned using ultrasonic vibration.A dry slip abrasion test was carried out on an HT-1000 spherical disc high-temperature tribometer based on the ASTM standard G99-95.Results and Discussions The number of small pores around the contact area significantly reduced with increased laser power.Comparisons of samples before and after LSP show that the strained areas exhibit inhomogeneous surfaces(Fig.2).With increasing laser power,the microhardness gradually increases;LSP significantly improves the microhardness of the LDED repair layer(Fig.4).The LDED-1200 W specimen has broad martensitic laths with a small number of fine needles;in comparison,in the LDED-1800 W specimen,the lath size decreases,the grain boundaries increase significantly,and internal refinement occurs with some dislocation(Fig.7).LSP induces significant refinement of surface grains,forming tiny nanoparticles with non-sequential orientation;the impact extends downward along the depth,and a large number of discrete dislocation structures,including dislocation tangles and cells,were found near the impact surface(Fig.8).The LDED specimen has a large worn area,with deep grooves and ridges parallel to the sliding direction,and almost the entire worn area is severely abraded(Fig.11);conversely,the worn surface of the LDED+LSP specimen is smooth,with only a small number of scratches and grooves in the middle of the wear,no large worn area,and no obvious adhesion phenomenon on the surface(Fig.12).Conclusions A combination of LDED and LSP post-treatment was used to repair damaged 45 steel.The main conclusions are as follows:(1)With increased LDED laser power,the powder is fully dissolved under high heat,the forming quality of the repair layer is improved,the quantity of internal holes is reduced,the porosity is reduced,the martensite lath-like structure is refined,and the cementite in the structure is dissolved.(2)Plastic deformation of the material occurs under the influence of LSP and the surface grains undergo refinement,forming nanograins with an approximate size of 30-50 nm.Subsequently,the deformation influence extends along the depth,generating many dislocations and forming high-density dislocation structures.(3)The main wears on the LDED-restored layer are plowing and adhesive wears,with a small contribution from abrasive wear;whereas the main wear mechanism of the LDED+LSP-restored layer is adhesive wear accompanied by abrasive wear.(4)LSP induces nanograin and dislocation reinforcement to refine the material structure,which effectively eliminated the internal pores,compacted the structure,and realized surface hardening,thus improving wear resistance.Meanwhile,the post-treatment process is accompanied by the dissolution of primary cementite,which further improves wear resistance.