Additive Manufacturing (AM) of metals allows the production of parts with complex designs, offeringadvanced properties if the evolution of the texture can be controlled. 17-4 precipitation hardening (PH)stainless stee...Additive Manufacturing (AM) of metals allows the production of parts with complex designs, offeringadvanced properties if the evolution of the texture can be controlled. 17-4 precipitation hardening (PH)stainless steel is a high strength, high corrosion resistance alloy used in a range of industries suitable forAM, such as aerospace and marine. Despite 17-4 PH being one of the most common steels for AM, thereare still gaps in the understanding of its AM processing–structure relationships. These include the natureof the matrix phase, as well as the development of texture through AM builds under different processingconditions. We have investigated how changing the laser power and scanning strategy affects the microstructure of 17-4 PH during laser powder bed fusion. It is revealed that the matrix phase is δ-ferritewith a limited austenite presence, mainly in regions of the microstructure immediately below melt pools.Austenite fraction is independent of the printing pattern and laser power. However, reducing the timebetween adjacent laser passes during printing results in an increase in the austenite volume fraction.Another effect of the higher laser power, as well as additional remelting within the printing strategy, isan increase in the average grain size by epitaxial ferrite grain growth across multiple build layers andthe development of a mosaic type microstructure. Changes to the scanning strategy have significant impacts on the textures observed along the build direction, while (100) texture along the scanning directionis observed consistently. Mechanisms for texture formation and the mosaic structure are proposed thatpresents a pathway to the design of texture via AM process control.展开更多
17-4 precipitation hardening(PH)stainless steel is a multi-purpose engineering alloy offering an excellent trade-off between strength,toughness,and corrosion properties.It is commonly employed in additive manufacturin...17-4 precipitation hardening(PH)stainless steel is a multi-purpose engineering alloy offering an excellent trade-off between strength,toughness,and corrosion properties.It is commonly employed in additive manufacturing via laser powder bed fusion owing to its good weldability.However,there are remaining gaps in the processing-structure-property relationships for AM 17-4 PH that need to be addressed.For instance,discrepancies in literature regarding the as-built microstructure,subsequent development of the matrix phase upon heat treatment,as well as the as-built residual stress should be addressed to enable reproducible printing of 17-4 builds with superior properties.As such,this work applies a comprehensive characterisation and testing approach to 17-4 PH builds fabricated with different processing parameters,both in the as-built state and after standard heat treatments.Tensile properties in as-built samples both along and normal to the build direction were benchmarked against standard wrought samples in the solution annealed and quenched condition(CA).When testing along the build direction,higher ductility was observed for samples produced with a higher laser power(energy density)due to the promotion of interlayer cohesion and,hence,reduction of interlayer defects.Following the CA heat treatment,the austenite volume fraction increased to∼35%,resulting in a lower yield stress and greater work hardening capacity than the as-built specimens due to the transformation induced plasticity effect.Neutron diffraction revealed a slight reduction in the magnitude of residual stress with laser power.A concentric scanning strategy led to a higher magnitude of residual stress than a bidirectional raster pattern.展开更多
基金supported under the Australian Research Council’s DECRA (project number DE180100440)the UNSW Scientia Fellowship schemes
文摘Additive Manufacturing (AM) of metals allows the production of parts with complex designs, offeringadvanced properties if the evolution of the texture can be controlled. 17-4 precipitation hardening (PH)stainless steel is a high strength, high corrosion resistance alloy used in a range of industries suitable forAM, such as aerospace and marine. Despite 17-4 PH being one of the most common steels for AM, thereare still gaps in the understanding of its AM processing–structure relationships. These include the natureof the matrix phase, as well as the development of texture through AM builds under different processingconditions. We have investigated how changing the laser power and scanning strategy affects the microstructure of 17-4 PH during laser powder bed fusion. It is revealed that the matrix phase is δ-ferritewith a limited austenite presence, mainly in regions of the microstructure immediately below melt pools.Austenite fraction is independent of the printing pattern and laser power. However, reducing the timebetween adjacent laser passes during printing results in an increase in the austenite volume fraction.Another effect of the higher laser power, as well as additional remelting within the printing strategy, isan increase in the average grain size by epitaxial ferrite grain growth across multiple build layers andthe development of a mosaic type microstructure. Changes to the scanning strategy have significant impacts on the textures observed along the build direction, while (100) texture along the scanning directionis observed consistently. Mechanisms for texture formation and the mosaic structure are proposed thatpresents a pathway to the design of texture via AM process control.
基金Funding by the AUSMURI program,Department of Industry,In-novation and Science,Australia is acknowledged.
文摘17-4 precipitation hardening(PH)stainless steel is a multi-purpose engineering alloy offering an excellent trade-off between strength,toughness,and corrosion properties.It is commonly employed in additive manufacturing via laser powder bed fusion owing to its good weldability.However,there are remaining gaps in the processing-structure-property relationships for AM 17-4 PH that need to be addressed.For instance,discrepancies in literature regarding the as-built microstructure,subsequent development of the matrix phase upon heat treatment,as well as the as-built residual stress should be addressed to enable reproducible printing of 17-4 builds with superior properties.As such,this work applies a comprehensive characterisation and testing approach to 17-4 PH builds fabricated with different processing parameters,both in the as-built state and after standard heat treatments.Tensile properties in as-built samples both along and normal to the build direction were benchmarked against standard wrought samples in the solution annealed and quenched condition(CA).When testing along the build direction,higher ductility was observed for samples produced with a higher laser power(energy density)due to the promotion of interlayer cohesion and,hence,reduction of interlayer defects.Following the CA heat treatment,the austenite volume fraction increased to∼35%,resulting in a lower yield stress and greater work hardening capacity than the as-built specimens due to the transformation induced plasticity effect.Neutron diffraction revealed a slight reduction in the magnitude of residual stress with laser power.A concentric scanning strategy led to a higher magnitude of residual stress than a bidirectional raster pattern.
