An innovative physical simulation apparatus, including high speed camera, red thermal imaging system, and mechanical quantity sensor, was used to investigate the friction heat generation and atom diffusion behavior du...An innovative physical simulation apparatus, including high speed camera, red thermal imaging system, and mechanical quantity sensor, was used to investigate the friction heat generation and atom diffusion behavior during Mg-Ti friction welding process. The results show that the friction coefficient mainly experiences two steady stages. The first steady stage corresponds to the Coulomb friction with material abrasion. The second steady stage corresponds to the stick friction with fully plastic flow. Moreover, the increasing rates of axial displacement, temperature and friction coefficient are obviously enhanced with the increase of rotation speed and axial pressure. It can also be found that the there exists rapid diffusion phenomenon in the Mg-Ti friction welding system. The large deformation activated diffusion coefficient is about 105 higher than that activated by thermal.展开更多
The present research is focused on the effects of standard heat treatment on the microstructure and mechanical properties of diffusion brazed IN-738 LC superalloy.Three distinct heat treatment cycles of full solution ...The present research is focused on the effects of standard heat treatment on the microstructure and mechanical properties of diffusion brazed IN-738 LC superalloy.Three distinct heat treatment cycles of full solution annealing,partial solution annealing,and aging treatment were applied to the bonded specimens,sequentially.The results reveal that bonding at 1120℃for 5 min leads to incomplete isothermal solidification and formation of eutectic phases including Ni-and Cr-rich borides in the joint centerline.Increasing the holding time to 45 min leads to the full isothermal solidification and formation of a nickel proeutectic solid-solution phase(γ)in the joints.The standard heat treatment of isothermally solidified and non-isothermally solidified specimens results in the complete elimination of the boride phases in the diffusion-affected zone and also the formation ofγ’precipitates in the isothermally solidified zone.However,discontinuously re-solidified products are observed in joint district in the non-isothermally solidified sample.The highest shear strength(~801 MPa)is achieved for isothermally solidified specimen after standard heat treatment;this strength is approximately 99%that of the substrate material.展开更多
Diffusion bonding of as-cast Mg−6Gd−3Y magnesium alloy was carried out at temperatures of 400−480℃ with bonding pressure of 6 MPa for 90 min.Diffusion bonded joints were solution treated at 495℃ for 14 h and then ag...Diffusion bonding of as-cast Mg−6Gd−3Y magnesium alloy was carried out at temperatures of 400−480℃ with bonding pressure of 6 MPa for 90 min.Diffusion bonded joints were solution treated at 495℃ for 14 h and then aged at 200℃ for 30 h.Microstructures and mechanical properties of joints were analyzed.The results showed that rare earth elements and their compounds gathering at bonding interface hindered the grain boundary migration crossing bonding interface.Tensile strength of as-bonded and as-solution treated joints increased firstly and then decreased with the bonding temperature increasing due to the combined effects of grain coarsening and solid-solution strengthening.As-bonded and solution-treated joints fractured at matrix except the joint bonded at 400℃,while aged joints fractured at bonding interface.The highest ultimate tensile strength of 279 MPa with elongation of 2.8%was found in joint bonded at 440℃ with solution treatment followed by aging treatment.展开更多
基金Projects (51101126, 51071123) supported by the National Natural Science Foundation of ChinaProjects (20110491684, 2012T50817) supported by the China Postdoctoral Science FoundationProject (20110942K) supported by the Open Fund of State Key Laboratory of Powder Metallurgy of Central South University, China
文摘An innovative physical simulation apparatus, including high speed camera, red thermal imaging system, and mechanical quantity sensor, was used to investigate the friction heat generation and atom diffusion behavior during Mg-Ti friction welding process. The results show that the friction coefficient mainly experiences two steady stages. The first steady stage corresponds to the Coulomb friction with material abrasion. The second steady stage corresponds to the stick friction with fully plastic flow. Moreover, the increasing rates of axial displacement, temperature and friction coefficient are obviously enhanced with the increase of rotation speed and axial pressure. It can also be found that the there exists rapid diffusion phenomenon in the Mg-Ti friction welding system. The large deformation activated diffusion coefficient is about 105 higher than that activated by thermal.
基金support from Ferdowsi University of Mashhad(FUM)under the research scheme(No.2/45210)。
文摘The present research is focused on the effects of standard heat treatment on the microstructure and mechanical properties of diffusion brazed IN-738 LC superalloy.Three distinct heat treatment cycles of full solution annealing,partial solution annealing,and aging treatment were applied to the bonded specimens,sequentially.The results reveal that bonding at 1120℃for 5 min leads to incomplete isothermal solidification and formation of eutectic phases including Ni-and Cr-rich borides in the joint centerline.Increasing the holding time to 45 min leads to the full isothermal solidification and formation of a nickel proeutectic solid-solution phase(γ)in the joints.The standard heat treatment of isothermally solidified and non-isothermally solidified specimens results in the complete elimination of the boride phases in the diffusion-affected zone and also the formation ofγ’precipitates in the isothermally solidified zone.However,discontinuously re-solidified products are observed in joint district in the non-isothermally solidified sample.The highest shear strength(~801 MPa)is achieved for isothermally solidified specimen after standard heat treatment;this strength is approximately 99%that of the substrate material.
基金financially supported by the Science Innovation Foundation of Shanghai Academy of Spaceflight Technology,China (No.SAST2020-117)。
文摘Diffusion bonding of as-cast Mg−6Gd−3Y magnesium alloy was carried out at temperatures of 400−480℃ with bonding pressure of 6 MPa for 90 min.Diffusion bonded joints were solution treated at 495℃ for 14 h and then aged at 200℃ for 30 h.Microstructures and mechanical properties of joints were analyzed.The results showed that rare earth elements and their compounds gathering at bonding interface hindered the grain boundary migration crossing bonding interface.Tensile strength of as-bonded and as-solution treated joints increased firstly and then decreased with the bonding temperature increasing due to the combined effects of grain coarsening and solid-solution strengthening.As-bonded and solution-treated joints fractured at matrix except the joint bonded at 400℃,while aged joints fractured at bonding interface.The highest ultimate tensile strength of 279 MPa with elongation of 2.8%was found in joint bonded at 440℃ with solution treatment followed by aging treatment.
