WE43 is a high-strength magnesium alloy containing rare-earth elements such as Y,Gd and Nd.Nevertheless,how to further obtain the balance of strength and ductility,as well as the manufacture of complex structures is s...WE43 is a high-strength magnesium alloy containing rare-earth elements such as Y,Gd and Nd.Nevertheless,how to further obtain the balance of strength and ductility,as well as the manufacture of complex structures is still a dilemma for its engineering application.In this study,WE43 alloy samples withfine microstructures,high densification and excellent mechanical properties were successfully prepared by laser powder bed fusion(LPBF)additive manufacturing.The optimal process window was established,and the formation mechanisms of three types of porosity defects were revealed,namely lack-of-fusion pores,meltfluctuation-induced pores,and keyhole-induced pores.With the combined process of laser power of 200 W and scanning speed of 600 mm/s,samples with a high density of 99.89%were obtained.Furthermore,periodic heterogeneous microstructure was prepared along the build direction,i.e.,fine grains(∼4.1μm)at melt pool boundaries and coarse grain(∼23.6μm)inside melt pool.This was mainly due to the preferential precipitation of Zr and Mg_(3)(Gd,Nd)nano-precipitates at the melt pool boundaries providing nucleation sites for the grains.This special feature could provide an extra hetero-deformation induced(HDI)strengthening and retard fracture.The optimal tensile yield strength,ultimate tensile strength and elongation at break were 276±1 MPa,292±1 MPa and 6.1±0.2%,respectively.The obtained tensile properties were superior to those of other magnesium alloys and those fabricated by other processes.The solid solution strengthening(∼24.5%),grain boundary strengthening(∼14.4%)and HDI strengthening(∼32.2%)were the main sources of high yield strength.This work provides a guidance on studying the pore defect suppression and strengthening mechanisms of WE43 alloy and other magnesium alloys produced by LPBF.展开更多
Laser powder bed fusion(LPBF)is a potential additive manufacturing process to manufacture Invar 36 alloy components with complicated geometry.Whereas it inevitably introduces specific microstructures and pore defects,...Laser powder bed fusion(LPBF)is a potential additive manufacturing process to manufacture Invar 36 alloy components with complicated geometry.Whereas it inevitably introduces specific microstructures and pore defects,which will further influence the mechanical properties.Hence,aiming at exploring the LPBF process-related microstructures and pore defects,and especially their influences on the damage mechanism and mechanical properties,Invar 36 alloy was manufactured by LPBF under designed different laser scanning speeds.The microstructure observations reveal that higher scanning speeds lead to equiaxed and short columnar grains with higher dislocation density,while lower scanning speeds result in elongated columnar grains with lower dislocation density.The pore defects analyzed by X-ray computed tomography(XCT)suggest that the high laser scanning speed gives rise to numerous lamellar and large lack-of-fusion(LOF)pores,and the excessively low laser scanning speed produces relatively small keyhole pores with high sphericity.Moreover,the insitu XCT tensile tests were originally performed to evaluate the damage evolution and failure mechanism.Specifically,high laser scanning speed causes brittle fracture due to the rapid growth and coalescence of initial lamellar LOF pores along the scan-ning direction.Low laser scanning speed induces ductile fracture originating from unstable depressions in the surfaces,while metallurgical and keyhole pores have little impact on damage evolution.Eventually,the process-structure-property correlation is established.The presence of high volume fraction of lamel-lar LOF pores,resulting from high scanning speed,leads to inferior yield strength and ductility.Besides,specimens without LOF pores exhibit larger grain sizes and lower dislocation density at decreased scanning speeds,slightly reducing yield strength while slightly enhancing ductility.This understanding lays the foundation for widespread applications of LPBF-processed Invar 36 alloy.展开更多
It is difficult to establish structure-property relationships in a defective solid because of its inhomogeneous-geometry microstructure caused by defects. In the present research, the effects of pores and cracks on th...It is difficult to establish structure-property relationships in a defective solid because of its inhomogeneous-geometry microstructure caused by defects. In the present research, the effects of pores and cracks on the Young’s modulus of a defective solid are studied. Based on the law of the conservation of energy, mathematical formulations are proposed to indicate how the shape, size, and distribution of defects affect the effective Young’s modulus. In this approach, detailed equations are illustrated to represent the shape and size of defects on the effective Young’s modulus. Different from the results obtained from the traditional empirical analyses, mixture law or statistical method, for the first time, our results from the finite element method （FEM） and strict analytical calculation show that the influence of pore radius and crack length on the effective Young’s modulus can be quantified. It is found that the longest crack in a typical microstructure of ceramic coating dominates the contribution of the effective Young’s modulus in the vertical direction of the crack.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52275333,52375335 and U22A202494)the Stabilization Support Project of AVIC Manufacturing Technology Institute(No.KZ571801)+1 种基金the Knowledge Innovation Special Project of Wuhan(No.2022010801010302)the Fundamental Research Funds for the Central Universities(No.YCJJ20230359).
文摘WE43 is a high-strength magnesium alloy containing rare-earth elements such as Y,Gd and Nd.Nevertheless,how to further obtain the balance of strength and ductility,as well as the manufacture of complex structures is still a dilemma for its engineering application.In this study,WE43 alloy samples withfine microstructures,high densification and excellent mechanical properties were successfully prepared by laser powder bed fusion(LPBF)additive manufacturing.The optimal process window was established,and the formation mechanisms of three types of porosity defects were revealed,namely lack-of-fusion pores,meltfluctuation-induced pores,and keyhole-induced pores.With the combined process of laser power of 200 W and scanning speed of 600 mm/s,samples with a high density of 99.89%were obtained.Furthermore,periodic heterogeneous microstructure was prepared along the build direction,i.e.,fine grains(∼4.1μm)at melt pool boundaries and coarse grain(∼23.6μm)inside melt pool.This was mainly due to the preferential precipitation of Zr and Mg_(3)(Gd,Nd)nano-precipitates at the melt pool boundaries providing nucleation sites for the grains.This special feature could provide an extra hetero-deformation induced(HDI)strengthening and retard fracture.The optimal tensile yield strength,ultimate tensile strength and elongation at break were 276±1 MPa,292±1 MPa and 6.1±0.2%,respectively.The obtained tensile properties were superior to those of other magnesium alloys and those fabricated by other processes.The solid solution strengthening(∼24.5%),grain boundary strengthening(∼14.4%)and HDI strengthening(∼32.2%)were the main sources of high yield strength.This work provides a guidance on studying the pore defect suppression and strengthening mechanisms of WE43 alloy and other magnesium alloys produced by LPBF.
基金support of the National Natural Science Foundation of China(Grant Nos.12372133 and 12027901)supported by the Natural Science Foun-dation of Hunan Province(Grant No.2021JJ30085)+2 种基金the Science and Technology Innovation Program of Hunan Province(Grant No.2021RC30306)Open Research Fund of State Key Laboratory of Precision Manufacturing for Extreme Service Performance,Central South University(Grant No.Kfkt2021-01)the Fund of State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body(Grant No.52175012).
文摘Laser powder bed fusion(LPBF)is a potential additive manufacturing process to manufacture Invar 36 alloy components with complicated geometry.Whereas it inevitably introduces specific microstructures and pore defects,which will further influence the mechanical properties.Hence,aiming at exploring the LPBF process-related microstructures and pore defects,and especially their influences on the damage mechanism and mechanical properties,Invar 36 alloy was manufactured by LPBF under designed different laser scanning speeds.The microstructure observations reveal that higher scanning speeds lead to equiaxed and short columnar grains with higher dislocation density,while lower scanning speeds result in elongated columnar grains with lower dislocation density.The pore defects analyzed by X-ray computed tomography(XCT)suggest that the high laser scanning speed gives rise to numerous lamellar and large lack-of-fusion(LOF)pores,and the excessively low laser scanning speed produces relatively small keyhole pores with high sphericity.Moreover,the insitu XCT tensile tests were originally performed to evaluate the damage evolution and failure mechanism.Specifically,high laser scanning speed causes brittle fracture due to the rapid growth and coalescence of initial lamellar LOF pores along the scan-ning direction.Low laser scanning speed induces ductile fracture originating from unstable depressions in the surfaces,while metallurgical and keyhole pores have little impact on damage evolution.Eventually,the process-structure-property correlation is established.The presence of high volume fraction of lamel-lar LOF pores,resulting from high scanning speed,leads to inferior yield strength and ductility.Besides,specimens without LOF pores exhibit larger grain sizes and lower dislocation density at decreased scanning speeds,slightly reducing yield strength while slightly enhancing ductility.This understanding lays the foundation for widespread applications of LPBF-processed Invar 36 alloy.
基金Project supported by the National Natural Science Foundation of China (Grant No. 50801005)
文摘It is difficult to establish structure-property relationships in a defective solid because of its inhomogeneous-geometry microstructure caused by defects. In the present research, the effects of pores and cracks on the Young’s modulus of a defective solid are studied. Based on the law of the conservation of energy, mathematical formulations are proposed to indicate how the shape, size, and distribution of defects affect the effective Young’s modulus. In this approach, detailed equations are illustrated to represent the shape and size of defects on the effective Young’s modulus. Different from the results obtained from the traditional empirical analyses, mixture law or statistical method, for the first time, our results from the finite element method （FEM） and strict analytical calculation show that the influence of pore radius and crack length on the effective Young’s modulus can be quantified. It is found that the longest crack in a typical microstructure of ceramic coating dominates the contribution of the effective Young’s modulus in the vertical direction of the crack.
