选区激光熔化成形Ti6Al4V合金拉伸性能提高的研究
|
摘要
目的提高选区激光熔化(SLM)成形Ti6Al4V合金的成形态延伸率,使成形态组织的拉伸性能接近或达到锻件标准。方法采用原位分解的方法,通过调节SLM成形过程中的工艺参数,如激光功率、能量密度、层厚、支撑所占面积比等,使已成形层中的针状α'马氏体在温度场作用下分解成α+β相。利用微观组织分析(SEM)、物相分析(XRD)和拉伸性能测试,明确Ti6Al4V合金发生原位分解的条件。结果增加SLM制造的层厚(60μm),提高激光功率(375 W),有利于降低SLM制造过程中的冷却速度和温度梯度,使马氏体组织发生a'→a+b相变。SEM和XRD结果表明,Ti6Al4V合金原位分解后的成形态显微组织由针状α相和颗粒状β相构成,不同于高温梯度和极快冷却速度下的常规SLM成形态组织。拉伸性能测试结果表明,Ti6Al4V经过原位分解后,在提高延伸率的同时,仍保持高屈服强度,屈服强度达到1100MPa以上,延伸率达到8%。断裂机制为韧性断裂。结论 SLM成形的Ti6Al4V合金经原位分解后,拥有更好的韧性,成形态的拉伸性能得到提高。
The work aims to improve the elongation of Ti6 Al4 V alloy formed by selective laser melting(SLM), so that the tensile properties of the formed structure can approach or meet the forging standard. The in-situ decomposition method was used to decompose the acicular α' martensite in the formed layer into α+β phase by adjusting the process parameters such as laser power, energy density, thickness of the layer and the area ratio of the support in the SLM forming process under the thermal cycle of heat source reciprocating motion for reciprocating heating and cooling. By means of microstructure observations(SEM),phase analysis(XRD) and tensile test, the conditions for in-situ decomposition of Ti6 Al4 V alloy were determined. Increasing the thickness of SLM layer(60 μm) and laser power(375 W) was beneficial to reducing the cooling rate and temperature gradient in SLM manufacturing process, resulting in a'→a+b transformation of martensite structure. The results of SEM and XRD showed that the morphology of Ti6 Al4 V alloy after in-situ decomposition was composed of acicular α phase and granular βphase, which was different from that of conventional SLM at high temperature gradient and extremely fast cooling rate. The tensile test results showed that the elongation of Ti6 Al4 V specimens increased while high yield strength was maintained after in-situ decomposition. The yield strength reached more than 1100 MPa, and the elongation reached 8%. The fracture mechanism was ductile fracture. SLM-formed Ti6 Al4 V alloy has better toughness after in-situ decomposition, which can improve the tensile properties of Ti6 Al4 V alloy.
The work aims to improve the elongation of Ti6 Al4 V alloy formed by selective laser melting(SLM), so that the tensile properties of the formed structure can approach or meet the forging standard. The in-situ decomposition method was used to decompose the acicular α' martensite in the formed layer into α+β phase by adjusting the process parameters such as laser power, energy density, thickness of the layer and the area ratio of the support in the SLM forming process under the thermal cycle of heat source reciprocating motion for reciprocating heating and cooling. By means of microstructure observations(SEM),phase analysis(XRD) and tensile test, the conditions for in-situ decomposition of Ti6 Al4 V alloy were determined. Increasing the thickness of SLM layer(60 μm) and laser power(375 W) was beneficial to reducing the cooling rate and temperature gradient in SLM manufacturing process, resulting in a'→a+b transformation of martensite structure. The results of SEM and XRD showed that the morphology of Ti6 Al4 V alloy after in-situ decomposition was composed of acicular α phase and granular βphase, which was different from that of conventional SLM at high temperature gradient and extremely fast cooling rate. The tensile test results showed that the elongation of Ti6 Al4 V specimens increased while high yield strength was maintained after in-situ decomposition. The yield strength reached more than 1100 MPa, and the elongation reached 8%. The fracture mechanism was ductile fracture. SLM-formed Ti6 Al4 V alloy has better toughness after in-situ decomposition, which can improve the tensile properties of Ti6 Al4 V alloy.
引文
[1]曹玄扬.多孔网格结构的拓扑优化设计及SLM制造[D].北京:北京工业大学,2016.CAO Xuan-yang.Topological optimization design and SLM manufacturing of porous grid structures[D].Beijing:Beijing University of Technology,2016.
[2]XU Y,ZHANG D,ZHOU Y,et al.Study on topology optimization design,manufacturability,and performance evaluation of Ti-6Al-4V porous structures fabricated by selective laser melting(SLM)[J].Materials,2017,10(9):1048.
[3]SHUMMUGAVEL M,POLISHETTY A,LITTLEFAIRG.Microstructure and mechanical properties of wrought and additive manufactured Ti-6Al-4V cylindrical bars[J].Procedia Technology,2015,20:231-236.
[4]QIU C L,ADKINS N J E,ATTALLAH M M.Microstructure and tensile properties of selectively laser-melted and of HIPed laser-melted Ti-6Al-4V[J].Materials science and engineering A,2013,578(8):230-239.
[5]RAFI H K,KARTHI N V,GONG H,et al.Microstructures and mechanical properties of Ti6Al4V parts fabricated by selective laser melting and electron beam melting[J].Journal of materials engineering&performance,2013,22(12):3872-3883.
[6]LU S,TANG H,NING Y,et al.Microstructure and mechanical properties of long Ti-6Al-4V rods additively manufactured out of a deep powder bed by selective electron beam melting with and without subsequent hot isostatic pressing[J].Metallurgical&materials transactions A,2015,46(9):3824-3834.
[7]ALI H,MA L,GHADBEI H,et al.In-situ residual stress reduction,martensitic decomposition and mechanical properties enhancement through high temperature powder bed pre-heating of selective laser melted Ti6Al4V[J].Materials science&engineering A,2017,695:211-220.
[8]LEUDERS S,THONE M,RIEME A,et al.On the mechanical behaviour of titanium alloy TiAl6V4 manufactured by selective laser melting:fatigue resistance and crack growth performance[J].International journal of fatigue,2013,48(3):300-307.
[9]XU W,BRANDT M,SUN S,et al.Additive manufacturing of strong and ductile Ti6Al4V by selective laser melting via in situ martensite decomposition[J].Acta materialia,2015,85:74-84.
[10]XU W,SUN S,ELAMBASSERIL J,et al.Ti-6Al-4Vadditively manufactured by selective laser melting with superior mechanical properties[J].JOM,2015,67(3):668-673.
[11]XU W,LUI E W,PATERAS A,et al.In situ,tailoring microstructure in additively manufactured Ti-6Al-4V for superior mechanical performance[J].Acta Materialia,2017,125:390-400.
[12]LUI E W,XU W,PATERAS A,et al.New development in selective laser melting of Ti6Al4V:awider processing window for the achievement of fully lamellarα+β,microstructures[J].JOM,2017(1):1-5.
[13]ZHAO X,LI S,ZHANG M,et al.Comparison of the microstructures and mechanical properties of Ti6Al4Vfabricated by selective laser melting and electron beam melting[J].Materials&design,2016,95:21-31.
[14]杨光,王文东,钦兰云,等.退火处理及沉积方向对激光沉积TA15钛合金组织和性能的影响[J].稀有金属材料与工程,2016,45(12):3295-3301.YANG Guang,WANG Wen-dong,QIN Lan-yun,et al.Effect of annealing treatment and deposition direction on microstructure and properties of laser deposited TA15 titanium alloy[J].Rare metal materials and engineering,2016,45(12):3295-3301.
[15]孙晓敏,刘栋,汤海波,等.TC17钛合金构件激光直接成形固态相变行为及显微组织[J].稀有金属材料与工程,2013,42(4):724-729.SUN Xiao-min,LIU Dong,TANG Hai-bo,et al.Solidphase transformation behavior and microstructure of TC17 titanium alloy components by laser direct forming[J].Rare metal materials and engineering,2013,42(4):724-729.
[2]XU Y,ZHANG D,ZHOU Y,et al.Study on topology optimization design,manufacturability,and performance evaluation of Ti-6Al-4V porous structures fabricated by selective laser melting(SLM)[J].Materials,2017,10(9):1048.
[3]SHUMMUGAVEL M,POLISHETTY A,LITTLEFAIRG.Microstructure and mechanical properties of wrought and additive manufactured Ti-6Al-4V cylindrical bars[J].Procedia Technology,2015,20:231-236.
[4]QIU C L,ADKINS N J E,ATTALLAH M M.Microstructure and tensile properties of selectively laser-melted and of HIPed laser-melted Ti-6Al-4V[J].Materials science and engineering A,2013,578(8):230-239.
[5]RAFI H K,KARTHI N V,GONG H,et al.Microstructures and mechanical properties of Ti6Al4V parts fabricated by selective laser melting and electron beam melting[J].Journal of materials engineering&performance,2013,22(12):3872-3883.
[6]LU S,TANG H,NING Y,et al.Microstructure and mechanical properties of long Ti-6Al-4V rods additively manufactured out of a deep powder bed by selective electron beam melting with and without subsequent hot isostatic pressing[J].Metallurgical&materials transactions A,2015,46(9):3824-3834.
[7]ALI H,MA L,GHADBEI H,et al.In-situ residual stress reduction,martensitic decomposition and mechanical properties enhancement through high temperature powder bed pre-heating of selective laser melted Ti6Al4V[J].Materials science&engineering A,2017,695:211-220.
[8]LEUDERS S,THONE M,RIEME A,et al.On the mechanical behaviour of titanium alloy TiAl6V4 manufactured by selective laser melting:fatigue resistance and crack growth performance[J].International journal of fatigue,2013,48(3):300-307.
[9]XU W,BRANDT M,SUN S,et al.Additive manufacturing of strong and ductile Ti6Al4V by selective laser melting via in situ martensite decomposition[J].Acta materialia,2015,85:74-84.
[10]XU W,SUN S,ELAMBASSERIL J,et al.Ti-6Al-4Vadditively manufactured by selective laser melting with superior mechanical properties[J].JOM,2015,67(3):668-673.
[11]XU W,LUI E W,PATERAS A,et al.In situ,tailoring microstructure in additively manufactured Ti-6Al-4V for superior mechanical performance[J].Acta Materialia,2017,125:390-400.
[12]LUI E W,XU W,PATERAS A,et al.New development in selective laser melting of Ti6Al4V:awider processing window for the achievement of fully lamellarα+β,microstructures[J].JOM,2017(1):1-5.
[13]ZHAO X,LI S,ZHANG M,et al.Comparison of the microstructures and mechanical properties of Ti6Al4Vfabricated by selective laser melting and electron beam melting[J].Materials&design,2016,95:21-31.
[14]杨光,王文东,钦兰云,等.退火处理及沉积方向对激光沉积TA15钛合金组织和性能的影响[J].稀有金属材料与工程,2016,45(12):3295-3301.YANG Guang,WANG Wen-dong,QIN Lan-yun,et al.Effect of annealing treatment and deposition direction on microstructure and properties of laser deposited TA15 titanium alloy[J].Rare metal materials and engineering,2016,45(12):3295-3301.
[15]孙晓敏,刘栋,汤海波,等.TC17钛合金构件激光直接成形固态相变行为及显微组织[J].稀有金属材料与工程,2013,42(4):724-729.SUN Xiao-min,LIU Dong,TANG Hai-bo,et al.Solidphase transformation behavior and microstructure of TC17 titanium alloy components by laser direct forming[J].Rare metal materials and engineering,2013,42(4):724-729.