The effect of heat treatment and ionic nitriding on the microstructure and surface performance of a newly developed precipitation-hardenable martensitic steel designed for laser powder bed fusion(L-PBF)was investigate...The effect of heat treatment and ionic nitriding on the microstructure and surface performance of a newly developed precipitation-hardenable martensitic steel designed for laser powder bed fusion(L-PBF)was investigated.The alloy,formulated without cobalt or molybdenum and with reduced nickel content(~7 wt.%),exhibits a refined cellular microstructure in the as-built state,with localised elemental segregation and nanoscale precipitation.A full factorial experimental design was applied to assess the individual and interactive effects of austenitisation,ageing,and nitriding on hardness,adhesive wear resistance,and corrosion behaviour.Ageing promoted Ni3Ti-type precipitation and increased hardness by 82%relative to the as-built state.Ionic nitriding produced a~30µm hardened layer,enhanced surface hardness(HV10,test force of approximately 98.1 N),and reduced wear by up to 97%.However,this treatment significantly impaired corrosion resistance,lowering polarisation resistance by 89%and increasing the corrosion current density by a factor of 4.6.The absence of protective titanium oxides and the presence of nitriding-induced microcracks were identified as the main contributors to this degradation.These results suggest that ageing alone offers the most balanced post-processing strategy when wear and corrosion coexist,whereas nitriding should be restricted to applications dominated by surface wear.展开更多
文摘The effect of heat treatment and ionic nitriding on the microstructure and surface performance of a newly developed precipitation-hardenable martensitic steel designed for laser powder bed fusion(L-PBF)was investigated.The alloy,formulated without cobalt or molybdenum and with reduced nickel content(~7 wt.%),exhibits a refined cellular microstructure in the as-built state,with localised elemental segregation and nanoscale precipitation.A full factorial experimental design was applied to assess the individual and interactive effects of austenitisation,ageing,and nitriding on hardness,adhesive wear resistance,and corrosion behaviour.Ageing promoted Ni3Ti-type precipitation and increased hardness by 82%relative to the as-built state.Ionic nitriding produced a~30µm hardened layer,enhanced surface hardness(HV10,test force of approximately 98.1 N),and reduced wear by up to 97%.However,this treatment significantly impaired corrosion resistance,lowering polarisation resistance by 89%and increasing the corrosion current density by a factor of 4.6.The absence of protective titanium oxides and the presence of nitriding-induced microcracks were identified as the main contributors to this degradation.These results suggest that ageing alone offers the most balanced post-processing strategy when wear and corrosion coexist,whereas nitriding should be restricted to applications dominated by surface wear.
