The soft-hard combined structures involving varying microhardness on the specimen surface of grey cast iron,processed by bionic laser technology,exhibit excellent wear resistance under dry sliding condition.Both the p...The soft-hard combined structures involving varying microhardness on the specimen surface of grey cast iron,processed by bionic laser technology,exhibit excellent wear resistance under dry sliding condition.Both the primary phase(PP)and the laser-treated phase(LP)play pivotal roles in the wear performance of grey cast iron,in association with various combinations of PP and LP microhardness,originating from different laser processing and heat treatment.Owing to the optimized combination of microhardness,the result exhibits the dominant role of LP,with higher microhardness,in wear test,indicating that this technology,apart from producing complex structures,can also act as a design-process method to modify the tribological properties of grey cast iron,and thus providing a feasible approach to tailor the surface microhardness and to modify the wear performance of grey cast iron.Moreover,a threshold of wear resistance is obtained,while LP microhardness is above 900 HV;meanwhile,beyond it,the change of PP microhardness has only minor impact on wear performance.Finite element analysis shows that,in line with varying microhardness combination,distinct stress distribution on specimen surface is achieved,agreeing well with the good wear resistance and tailorable microhardness of LP and PP.展开更多
The external hard TiN ceramic layer and an internal reinforced NiTi matrix were controlled by combining nitriding and solution treatment to achieve ultra-high micro-hardness and excellent wear performance.In addition,...The external hard TiN ceramic layer and an internal reinforced NiTi matrix were controlled by combining nitriding and solution treatment to achieve ultra-high micro-hardness and excellent wear performance.In addition,the effects of nitriding and solution treatment on the microstructure evolution,martensitic transformation,and mechanical and functional properties of 60NiTi alloys were investigated.Compared with 60NiTi alloy,a harder TiN layer appeared at the surface of 60NiTi alloy with nitriding treatment.Meanwhile,a Ni_(3)Ti layer formed under the bottom of TiN layer owing to the consumption of Ti in matrix induced by formation of TiN layer.Upon undergoing solution treatment,the precipitates evolved from the coexistence of Ni_(3)Ti and Ni_(3)Ti_(2)phase to Ni_(4)Ti_(3)phase.The introduction of the outer harder TiN ceramic layer had a constraint of martensitic transformation of 60NiTi alloy,which led to the reduction of martensitic transformation temperature(Ms)and the suppression of martensitic transformation.Importantly,the construction of outermost harder TiN ceramic layer at the surface of B2-NiTi matrix enhanced Ni_(4)Ti_(3)phase improved significantly the microhardness and wear performances by the nitriding and followed solution treatment.Meanwhile,the high compressive fracture strength,fracture strain and superior superelasticity of 60NiTi alloy can be maintained.展开更多
In this study,AZ31 Mg alloy sheets were processed by a severe plastic deformation(SPD)technique called forging-bending repeated deformation(FBRD).The effect on the microstructure and microhardness of AZ31 Mg alloy thr...In this study,AZ31 Mg alloy sheets were processed by a severe plastic deformation(SPD)technique called forging-bending repeated deformation(FBRD).The effect on the microstructure and microhardness of AZ31 Mg alloy through FBRD was investigated with increasing temperature treatment and a 90°cross route.The results reveal that the effective strain increases with the number of passes.The flow uniformity is effectively enhanced due to alterations in shear deformation direction.After four passes of deformation,the average grain size is refined by 79.3%compared to the initial specimen.The grain refinement mechanism predominantly originates from the synergistic effects of discontinuous dynamic recrystallization(DDRX),continuous dynamic recrystallization(CDRX),and twinning-induced recrystallization(TDRX).The formation of{1012}extension twins(ET)significantly contributes to coarse grain subdivision and plastic deformation coordinated.Furthermore,pyramidal<c+a>slip activation effectively enhances the plasticity of Mg alloys.By post four-pass processing,the alloy exhibits a microhardness of 81.9HV,primarily governed by fine grain strengthening and dislocation strengthening mechanisms.展开更多
激光定向能量沉积(laser directed energy deposition,LDED)凭借高效率与工艺柔性,正成为解决室温高脆性和高活性的TiAl4822(Ti-48Al-2Cr-2Nb)合金传统工艺难加工、难制备大型复杂构件问题的关键途径,以充分发挥其航空发动机等高温轻质...激光定向能量沉积(laser directed energy deposition,LDED)凭借高效率与工艺柔性,正成为解决室温高脆性和高活性的TiAl4822(Ti-48Al-2Cr-2Nb)合金传统工艺难加工、难制备大型复杂构件问题的关键途径,以充分发挥其航空发动机等高温轻质部件的理想材料潜力。然而,LDED过程中快速熔融-凝固循环会产生极大的温度梯度和残余应力,从而导致构件开裂,但目前尚无成熟手段能够完全抑制裂纹产生。本工作利用整体高温辅助LDED制备出30 mm×25 mm×6 mm致密无裂纹的TiAl4822合金薄壁构件,并对其宏观形貌、微观组织、孔隙率及显微硬度进行研究。研究结果表明:在常温条件下,LDED制备的TiAl4822合金薄壁样件易发生以解理为主的脆性断裂,显微组织以细小等轴晶为主;引入800℃整体高温辅助后,沉积层晶粒定向生长为自下而上倾斜的柱状晶,孔隙率从0.05%降至0.008%,孔径分布更均匀,表面未见宏观裂纹;与此同时,显微硬度由常温样件的390.46HV_(0.2)降至354.94HV_(0.2),这主要归因于在高温辅助条件下晶粒长大、晶界减少及析出相中γ相的含量相对增加。因此,整体高温辅助不仅有效抑制裂纹与大尺寸孔隙的产生,还优化微观组织均匀性,为TiAl4822合金的高致密、高性能制备提供新途径。展开更多
A detailed investigation for the influence of post weld heat treatment （PWHT） on the microstructure of TC4 and TC17 dissimilar joints was analyzed. The fully transformed microstructure in the as-welded zone indicate...A detailed investigation for the influence of post weld heat treatment （PWHT） on the microstructure of TC4 and TC17 dissimilar joints was analyzed. The fully transformed microstructure in the as-welded zone indicated that the peak temperature exceeded theβ-transus temperature at the weld interface during linear friction welding. TC4 side was mainly composed of martensiteα′phase with random distribution and it was singleβfor that of TC17. In the thermomechanically affected zones of TC4 and TC17, the structure undergoes severe plastic deformation and re-orientation, yet without altering the phase fractions. After PWHT, in the weld zone of TC4 alloy, the phase transformationα′→α＋βoccurred and the acicularαwas coarsened, which resulted in a decrease in hardness. In the weld zone of TC17 alloy, fineαphase precipitated at the grain boundary and withinβgrains, which resulted in a sharp increase in hardness.展开更多
Directionally solidified （DS） specimens of Nb-Ti-Si based ultrahigh temperature alloy were heat-treated at （1 500 ℃, 50 h） and （1 500 ℃, 50 h） ＋ （1 100 ℃, 50 h）, respectively. The results show that the mic...Directionally solidified （DS） specimens of Nb-Ti-Si based ultrahigh temperature alloy were heat-treated at （1 500 ℃, 50 h） and （1 500 ℃, 50 h） ＋ （1 100 ℃, 50 h）, respectively. The results show that the microstructures become uniform, the long and big primary （Nb,X）sSi3 （X represents Ti and Hf elements） plates in the DS specimens are broken into small ones, and the eutectic cells lose their lamellar morphology and their interfaces become blurry after heat-treatment. Meanwhile, the （Nb,X）sSi3 slices in the eutectic cells of the DS specimens coarsen obviously after heat-treatment. Homogenizing and aging treatments could effectively eliminate elemental microsegregation, and the segregation ratios of all elements in niobium solid solution （Nbss） in different regions tend to 1. After heat-treatment, the microhardness of retained eutectic cells increases evidently, and the maximum value reaches HV1 404.57 for the specimen directionally solidified with a withdrawing rate of 100 μm/s and then heat-treated at （1 500 ℃, 50 h） ＋ （1 100 ℃, 50 h）, which is 72.8 % higher than that under DS condition.展开更多
The squeeze pressure field and power ultrasonic field were applied during the conventional casting process of Al-5.0Cu alloy simultaneously. The effects of individual squeeze pressure or power ultrasonic and their cou...The squeeze pressure field and power ultrasonic field were applied during the conventional casting process of Al-5.0Cu alloy simultaneously. The effects of individual squeeze pressure or power ultrasonic and their coupling on the microstructures and microhardness of Al-5.0Cu alloy were studied by optical microscopy, scanning electron microscopy, image analysis and micro Vickers hardness test. The results show that compared with the conventional casting, refined microstructures, homogeneous distribution of α（Al） and θ（Al2Cu） and improved microhardness can be obtained when squeeze pressure or power ultrasonic is applied individually. For the case of combined fields, both the treated region and the improvement of microstructure and properties can be enhanced.展开更多
利用等离子熔覆技术在低碳钢表面制备了不同C含量的Al_(1.5)CoCrFeNiNb_(0.2)C_(x)(x=0,0.01,0.02,0.05,0.2)高熵合金熔覆层,采用X射线衍射仪(X-ray diffraction,XRD)、扫描电镜(scanning electron microscope,SEM)、透射电镜(transmiss...利用等离子熔覆技术在低碳钢表面制备了不同C含量的Al_(1.5)CoCrFeNiNb_(0.2)C_(x)(x=0,0.01,0.02,0.05,0.2)高熵合金熔覆层,采用X射线衍射仪(X-ray diffraction,XRD)、扫描电镜(scanning electron microscope,SEM)、透射电镜(transmission electron microscopy,TEM)、硬度仪以及磨损试验机等手段,研究C含量对熔覆层微观组织以及力学性能的影响规律.结果表明,x=0,0.01时,Al_(1.5)CoCrFeNiNb_(0.2)C_(x)高熵合金的物相由BCC相以及少量富Nb的Laves相组成;x=0.02~0.2时,能够原位合成NbC,且随着C含量的升高,NbC的析出量逐渐增加.x=0,0.01时,高熵合金的微观组织为树枝晶结构,枝晶为BCC相,枝晶间为BCC相+富Nb的Laves相组成的共晶组织.x=0.02~0.2时,树枝晶基体上析出原位合成NbC,并且随着C含量的升高,NbC的析出量和尺寸逐渐增大,其形貌由低含量下(x=0.02,0.05)的颗粒状逐渐转变为高含量下(x=0.2)的颗粒状以及十字状.TEM表明,高熵合金基体与NbC增强相之间的界面光滑纯净,没有任何缺陷以及其他污染物.随着C含量由x=0增加至x=0.2,熔覆层硬度由560.1 HV增加至762.2 HV,磨损率由24.69 mg/min降低至4.70 mg/min.展开更多
基金supported by Project 985-High Performance Materials of Jilin University and the Project 985-Biomimetic Engineering Science and Technology Innovation and National Natural Science Foundation of China(No.51275200).
文摘The soft-hard combined structures involving varying microhardness on the specimen surface of grey cast iron,processed by bionic laser technology,exhibit excellent wear resistance under dry sliding condition.Both the primary phase(PP)and the laser-treated phase(LP)play pivotal roles in the wear performance of grey cast iron,in association with various combinations of PP and LP microhardness,originating from different laser processing and heat treatment.Owing to the optimized combination of microhardness,the result exhibits the dominant role of LP,with higher microhardness,in wear test,indicating that this technology,apart from producing complex structures,can also act as a design-process method to modify the tribological properties of grey cast iron,and thus providing a feasible approach to tailor the surface microhardness and to modify the wear performance of grey cast iron.Moreover,a threshold of wear resistance is obtained,while LP microhardness is above 900 HV;meanwhile,beyond it,the change of PP microhardness has only minor impact on wear performance.Finite element analysis shows that,in line with varying microhardness combination,distinct stress distribution on specimen surface is achieved,agreeing well with the good wear resistance and tailorable microhardness of LP and PP.
基金supported by the Development Plan of Shandong Province Young Innovation Team of Higher Education Institutions,China(No.2023KJ242)the National Natural Science Foundation of China(Nos.52371181,52101231,52101232,and 52175192)the Natural Science Foundation of Shandong Province,China(Nos.ZR2024QE019,and ZR2021QE044)。
文摘The external hard TiN ceramic layer and an internal reinforced NiTi matrix were controlled by combining nitriding and solution treatment to achieve ultra-high micro-hardness and excellent wear performance.In addition,the effects of nitriding and solution treatment on the microstructure evolution,martensitic transformation,and mechanical and functional properties of 60NiTi alloys were investigated.Compared with 60NiTi alloy,a harder TiN layer appeared at the surface of 60NiTi alloy with nitriding treatment.Meanwhile,a Ni_(3)Ti layer formed under the bottom of TiN layer owing to the consumption of Ti in matrix induced by formation of TiN layer.Upon undergoing solution treatment,the precipitates evolved from the coexistence of Ni_(3)Ti and Ni_(3)Ti_(2)phase to Ni_(4)Ti_(3)phase.The introduction of the outer harder TiN ceramic layer had a constraint of martensitic transformation of 60NiTi alloy,which led to the reduction of martensitic transformation temperature(Ms)and the suppression of martensitic transformation.Importantly,the construction of outermost harder TiN ceramic layer at the surface of B2-NiTi matrix enhanced Ni_(4)Ti_(3)phase improved significantly the microhardness and wear performances by the nitriding and followed solution treatment.Meanwhile,the high compressive fracture strength,fracture strain and superior superelasticity of 60NiTi alloy can be maintained.
基金Project(52174362)supported by the National Natural Science Foundation of ChinaProject(2023JJ10020)supported by the Natural Science Foundation of Hunan Province,China+2 种基金Project(2024RC7002)supported by the Science and Technology Innovation Program of Hunan Province,ChinaProject(2024CY2-GJHX-71)supported by the Shaanxi Provincial Key R&D Program,ChinaProject supported by the Yancheng“Talent Plan of Yellow Sea Pearl”for Leading Talent Project,China。
文摘In this study,AZ31 Mg alloy sheets were processed by a severe plastic deformation(SPD)technique called forging-bending repeated deformation(FBRD).The effect on the microstructure and microhardness of AZ31 Mg alloy through FBRD was investigated with increasing temperature treatment and a 90°cross route.The results reveal that the effective strain increases with the number of passes.The flow uniformity is effectively enhanced due to alterations in shear deformation direction.After four passes of deformation,the average grain size is refined by 79.3%compared to the initial specimen.The grain refinement mechanism predominantly originates from the synergistic effects of discontinuous dynamic recrystallization(DDRX),continuous dynamic recrystallization(CDRX),and twinning-induced recrystallization(TDRX).The formation of{1012}extension twins(ET)significantly contributes to coarse grain subdivision and plastic deformation coordinated.Furthermore,pyramidal<c+a>slip activation effectively enhances the plasticity of Mg alloys.By post four-pass processing,the alloy exhibits a microhardness of 81.9HV,primarily governed by fine grain strengthening and dislocation strengthening mechanisms.
文摘A detailed investigation for the influence of post weld heat treatment （PWHT） on the microstructure of TC4 and TC17 dissimilar joints was analyzed. The fully transformed microstructure in the as-welded zone indicated that the peak temperature exceeded theβ-transus temperature at the weld interface during linear friction welding. TC4 side was mainly composed of martensiteα′phase with random distribution and it was singleβfor that of TC17. In the thermomechanically affected zones of TC4 and TC17, the structure undergoes severe plastic deformation and re-orientation, yet without altering the phase fractions. After PWHT, in the weld zone of TC4 alloy, the phase transformationα′→α＋βoccurred and the acicularαwas coarsened, which resulted in a decrease in hardness. In the weld zone of TC17 alloy, fineαphase precipitated at the grain boundary and withinβgrains, which resulted in a sharp increase in hardness.
基金Project(51071124)supported by the National Natural Science Foundation of ChinaProject(CX200605)supported by the Doctorate Foundation of Northwestern Polytechnical University,ChinaProject(20096102110012)supported by a Special Research Fund for Doctoral Disciplines in Colleges and Universities of the Ministry of Education,China
文摘Directionally solidified （DS） specimens of Nb-Ti-Si based ultrahigh temperature alloy were heat-treated at （1 500 ℃, 50 h） and （1 500 ℃, 50 h） ＋ （1 100 ℃, 50 h）, respectively. The results show that the microstructures become uniform, the long and big primary （Nb,X）sSi3 （X represents Ti and Hf elements） plates in the DS specimens are broken into small ones, and the eutectic cells lose their lamellar morphology and their interfaces become blurry after heat-treatment. Meanwhile, the （Nb,X）sSi3 slices in the eutectic cells of the DS specimens coarsen obviously after heat-treatment. Homogenizing and aging treatments could effectively eliminate elemental microsegregation, and the segregation ratios of all elements in niobium solid solution （Nbss） in different regions tend to 1. After heat-treatment, the microhardness of retained eutectic cells increases evidently, and the maximum value reaches HV1 404.57 for the specimen directionally solidified with a withdrawing rate of 100 μm/s and then heat-treated at （1 500 ℃, 50 h） ＋ （1 100 ℃, 50 h）, which is 72.8 % higher than that under DS condition.
基金Project(51374110)supported by the National Natural Science Foundation of ChinaProject(2015A030312003)supported by the Natural Science Foundation of Guangdong Province for Research Team,China
文摘The squeeze pressure field and power ultrasonic field were applied during the conventional casting process of Al-5.0Cu alloy simultaneously. The effects of individual squeeze pressure or power ultrasonic and their coupling on the microstructures and microhardness of Al-5.0Cu alloy were studied by optical microscopy, scanning electron microscopy, image analysis and micro Vickers hardness test. The results show that compared with the conventional casting, refined microstructures, homogeneous distribution of α（Al） and θ（Al2Cu） and improved microhardness can be obtained when squeeze pressure or power ultrasonic is applied individually. For the case of combined fields, both the treated region and the improvement of microstructure and properties can be enhanced.
文摘利用等离子熔覆技术在低碳钢表面制备了不同C含量的Al_(1.5)CoCrFeNiNb_(0.2)C_(x)(x=0,0.01,0.02,0.05,0.2)高熵合金熔覆层,采用X射线衍射仪(X-ray diffraction,XRD)、扫描电镜(scanning electron microscope,SEM)、透射电镜(transmission electron microscopy,TEM)、硬度仪以及磨损试验机等手段,研究C含量对熔覆层微观组织以及力学性能的影响规律.结果表明,x=0,0.01时,Al_(1.5)CoCrFeNiNb_(0.2)C_(x)高熵合金的物相由BCC相以及少量富Nb的Laves相组成;x=0.02~0.2时,能够原位合成NbC,且随着C含量的升高,NbC的析出量逐渐增加.x=0,0.01时,高熵合金的微观组织为树枝晶结构,枝晶为BCC相,枝晶间为BCC相+富Nb的Laves相组成的共晶组织.x=0.02~0.2时,树枝晶基体上析出原位合成NbC,并且随着C含量的升高,NbC的析出量和尺寸逐渐增大,其形貌由低含量下(x=0.02,0.05)的颗粒状逐渐转变为高含量下(x=0.2)的颗粒状以及十字状.TEM表明,高熵合金基体与NbC增强相之间的界面光滑纯净,没有任何缺陷以及其他污染物.随着C含量由x=0增加至x=0.2,熔覆层硬度由560.1 HV增加至762.2 HV,磨损率由24.69 mg/min降低至4.70 mg/min.
