By means of the positron annihilation technique (PAT), superfine TiC powders obtained by ball-milling process were characterized. The results showed that there was a clear correlation between the change in TiC powders...By means of the positron annihilation technique (PAT), superfine TiC powders obtained by ball-milling process were characterized. The results showed that there was a clear correlation between the change in TiC powders and that in the PAT parameters. In the high energy ball-milling process, TiC powders were severely deformed, which caused large increase in the amount of defects and severe distortion of lattice. On the other hand, the extreme refinement of grain size of powders resulted in the increase of grain boundary area and enhancement of system free energy. The spacing between deformed domains in 96 h milled samples is somewhat smaller than those in 48 h milled samples, indicating the size of Type II defects in 96 h milled samples is somewhat smaller than that in 48 h milled samples.展开更多
The conditions of heating and cooling of piercing mandrels made of 4X5MFS steel of a three-roll screw mill 30-80 in the production of a closed cavity of steel vessels of small volume are determined.It is established t...The conditions of heating and cooling of piercing mandrels made of 4X5MFS steel of a three-roll screw mill 30-80 in the production of a closed cavity of steel vessels of small volume are determined.It is established that multiple cycles of heating up to 600℃ and cooling with water up to 80℃ for about 7 seconds/1 cycle lead to the formation of ridges,shells and cracks on the surface and in the volume of the tool.The loss of structural strength of the material leads to the breakdown of the mandrel during the stitching process.The technique and equipment of magnetic powder control have been developed to establish the dynamics of the growth of internal and external defects of mandrels.An equation is obtained that allows determining the increase in the number of defects in the sewing tool of a screw rolling mill.The technology of non-destructive testing made it possible to develop a rational plan for replacing the sewing mandrels,which allows for predicting the appearance of defects leading to a complex breakdown of the deforming tool at the NPO Pribor machine-building enterprise.展开更多
钛及其合金的粉末床熔融式(PBF)增材制造技术因具有定制制造、成本节约和时间优化等优势,在航空以及生物医学领域备受关注。但在PBF制造钛合金时,多种因素如热导率低、热积累、氧化敏感性及快速冷却引起的热应力共同导致成形件缺陷、组...钛及其合金的粉末床熔融式(PBF)增材制造技术因具有定制制造、成本节约和时间优化等优势,在航空以及生物医学领域备受关注。但在PBF制造钛合金时,多种因素如热导率低、热积累、氧化敏感性及快速冷却引起的热应力共同导致成形件缺陷、组织差异、性能不稳定与质量参差不齐等问题。因此,本文通过调研PBF技术中的激光粉末床熔融(Laser powder bed fusion,L-PBF)和电子束粉末床熔融(Electron beam powder bed fusion,EB-PBF)技术原理,讨论PBF增材制造钛合金微观组织特征、力学性能、耐腐蚀性能、耐磨损性能与生物相容性的特点;同时,聚焦成形过程中的缺陷形成机理及影响,提出缺陷消除方法;最后,展望两种技术的未来发展方向,为促进创新钛合金增材制造提供新的研究思路。展开更多
基金This research is jointly financially supported by the National Natural Science Foundation of China, the Doctoral Edu-cation F
文摘By means of the positron annihilation technique (PAT), superfine TiC powders obtained by ball-milling process were characterized. The results showed that there was a clear correlation between the change in TiC powders and that in the PAT parameters. In the high energy ball-milling process, TiC powders were severely deformed, which caused large increase in the amount of defects and severe distortion of lattice. On the other hand, the extreme refinement of grain size of powders resulted in the increase of grain boundary area and enhancement of system free energy. The spacing between deformed domains in 96 h milled samples is somewhat smaller than those in 48 h milled samples, indicating the size of Type II defects in 96 h milled samples is somewhat smaller than that in 48 h milled samples.
文摘The conditions of heating and cooling of piercing mandrels made of 4X5MFS steel of a three-roll screw mill 30-80 in the production of a closed cavity of steel vessels of small volume are determined.It is established that multiple cycles of heating up to 600℃ and cooling with water up to 80℃ for about 7 seconds/1 cycle lead to the formation of ridges,shells and cracks on the surface and in the volume of the tool.The loss of structural strength of the material leads to the breakdown of the mandrel during the stitching process.The technique and equipment of magnetic powder control have been developed to establish the dynamics of the growth of internal and external defects of mandrels.An equation is obtained that allows determining the increase in the number of defects in the sewing tool of a screw rolling mill.The technology of non-destructive testing made it possible to develop a rational plan for replacing the sewing mandrels,which allows for predicting the appearance of defects leading to a complex breakdown of the deforming tool at the NPO Pribor machine-building enterprise.
文摘钛及其合金的粉末床熔融式(PBF)增材制造技术因具有定制制造、成本节约和时间优化等优势,在航空以及生物医学领域备受关注。但在PBF制造钛合金时,多种因素如热导率低、热积累、氧化敏感性及快速冷却引起的热应力共同导致成形件缺陷、组织差异、性能不稳定与质量参差不齐等问题。因此,本文通过调研PBF技术中的激光粉末床熔融(Laser powder bed fusion,L-PBF)和电子束粉末床熔融(Electron beam powder bed fusion,EB-PBF)技术原理,讨论PBF增材制造钛合金微观组织特征、力学性能、耐腐蚀性能、耐磨损性能与生物相容性的特点;同时,聚焦成形过程中的缺陷形成机理及影响,提出缺陷消除方法;最后,展望两种技术的未来发展方向,为促进创新钛合金增材制造提供新的研究思路。
