Co-reporter:G.B. Niu, D.P. Wang, Z.W. Yang, Y. Wang
Ceramics International 2017 Volume 43(Issue 1) pp:439-450
Publication Date(Web):January 2017
DOI:10.1016/j.ceramint.2016.09.178
Abstract
In this manuscript, Al2O3 ceramic and TiAl alloy were brazed with Ag-Cu-Ti based composite fillers containing B powder additive. The effects of B content, Ti content, and the brazing temperature on the microstructure and mechanical properties of the brazed joints were investigated. The typical interfacial microstructure of the brazed joint was: Al2O3/Ti3(Cu, Al)3O/Ag(s.s)+TiB+Ti(Cu, Al)+fine AlCu2Ti/blocky AlCu2Ti+AlCuTi/TiAl. TiB whiskers synthesized in situ by the reaction of the B additive with Ti, served as nucleation sites for the formation of fine Ti(Cu, Al) and AlCu2Ti grains and improved the bonding properties. With increasing B content, more fine-grains were formed in the brazing seam and the thickness of the Ti3(Cu, Al)3O reaction layer adjacent to the Al2O3 ceramic decreased. Brazing parameters also influenced the joint microstructure. Growth of Ti3(Cu, Al)3O layer and AlCu2Ti formed with increase in brazing temperature. Moreover, the formation of dispersed fine-grains in the brazing seam depended largely on the initial Ti content in the composite filler. With increase in initial Ti content, the TiB-reinforced area was broadened while the blocky AlCu2Ti content decreased gradually. The maximum shear strength of Al2O3/TiAl joint brazed with B-reinforced composite filler was 148 MPa, which was 246% higher than that brazed without B addition. The joint shear strength was determined by the combined influences of the thermal expansion mismatch between the joined materials, the thickness of the Ti3(Cu, Al)3O layer, and the presence of defects in the joints.
Co-reporter:Yi Tong Lin, Ming Chao Wang, Yu Zhang, Ya Zhang He, Dong Po Wang
Materials & Design 2017 Volume 113(Volume 113) pp:
Publication Date(Web):5 January 2017
DOI:10.1016/j.matdes.2016.10.010
•Aluminum alloy 2219 was welded by variable polarity tungsten inert gas arc welding.•The effect of post-weld heat treatment on morphologies of precipitates was studied in detail.•The cryogenic fracture toughness of the weld metal was investigated by crack tip opening displacement tests.•The crack tip opening displacement values at 77 K were nearly 20% higher than those at 298 K.In this work, the effect of post-weld heat treatment (solid solution + artificial aging) on the microstructure and cryogenic fracture toughness of the weld metal of VPTIG welded AA2219 joints were investigated by using crack tip opening displacement (CTOD) test method. The samples were divided into three types: (i) the weld metal of as-welded joint, marked as sample A; (ii) the weld metal of post-weld heat treated joint, marked as sample B; (iii) the base metal used for comparison, marked as BM. The results showed that the solution treatment dissolved θ phases, and the artificial aging treatment re-precipitated θ' phases. After post-weld heat treatment, the strength of weld metal was improved, accompanied with a little bit of decrease in the plasticity and fracture toughness. No matter what kind of sample types, compared to 298 K, the strength tested at 77 K was higher due to the weaker lattice vibration frequency and lower energy fluctuation. Besides, the plasticity was also higher at 77 K than that at 298 K, because the Peierls-Nabarro force was not sensitive to temperatures. Thus, the fracture toughness was also better at 77 K.Download high-res image (110KB)Download full-size image
Co-reporter:Yanyan Feng, Shengsun Hu, Dongpo Wang, Hai Zhang
Vacuum 2016 Volume 132() pp:22-30
Publication Date(Web):October 2016
DOI:10.1016/j.vacuum.2016.07.021
•Fold defects were a key factor determining surface quality and fatigue life.•Widths of surface topography and indentations were critical to fold defect formation.•The depth of surface morphology D determines the dimension of fold defects.Five groups of D36 steel plates with different surface topographies were prepared to evaluate the influence of topography and needle size on the surface quality after ultrasonic peening treatment. Factors such as the stress distribution, micro-hardness, and fold defects were studied to quantify the surface quality. In addition, ABAQUS/Explicit finite element modeling was employed to simulate the peening process. The numerical results revealed that fold overlapping was dependent on the initial surface topography and the size of the peening needle could influence the morphology of the fold defects. The results further indicated that fold defects were closely related to the initial surface topography, with the aspect ratio being a key determining factor for the dimensions of fold defects.
Co-reporter:Yang Liu, Dongpo Wang, Caiyan Deng, Lixing Huo, Lijun Wang, Shu Cao
Materials & Design 2014 63() pp: 488-492
Publication Date(Web):
DOI:10.1016/j.matdes.2014.06.061
Co-reporter:Xiaohui Zhao, Dongpo Wang, Lixing Huo
Materials & Design 2011 Volume 32(Issue 1) pp:88-96
Publication Date(Web):January 2011
DOI:10.1016/j.matdes.2010.06.030
Contrast fatigue tests were carried out on T-shape tubular joints of 20 steel in three conditions: as welded, treated by ultrasonic peening treatment (UPT) before loading and UPT under loading. Results are: (1) Dispersity of test results measured by nominal stress is much larger than that measured by hot spot stress. After UPT before loading, fatigue strength of 20 steel tubular joints measured by hot spot stress increases by 67% and fatigue life is prolonged by 22–45 times. (2) Under low stress ratio R, UPT before loading can improve the fatigue performance of welded tubular joints significantly. (3) Under high stress ratio R, UPT under loading (static load) is recommended to improve the fatigue performance of welded tubular joints. UPT under loading not only enhances the fatigue properties at low stress level, but also at high stress level. (4) The general rule of S–N curves of welded joints treated by UPT is commonly effected by external load (static load) and self release of residual stress.
Co-reporter:Danqing Yin, Dongpo Wang, Hongyang Jing, Lixing Huo
Materials & Design (1980-2015) 2010 Volume 31(Issue 7) pp:3299-3307
Publication Date(Web):August 2010
DOI:10.1016/j.matdes.2010.02.006
The conventional fatigue design codes was formulated based on the data from test stress cycles less than 1 × 107. Most of them could not be applied for welded structures serviced in the ultra-long life region so the new recommendations were discussed. The method of ultrasonic peening treatment (UPT) was introduced in this thesis as a post-weld treatment to improve the fatigue strength of the welded structures. The fatigue behavior of welded structures in the ultra-long life region was investigated using an ultrasonic fatigue test machine under two post-weld treatment states: the as-welded and the UPT. Discussion had also been made about the fracture mechanism on the UPT joints in ultra-long life fatigue test.
