Papers by Keyword: Interfacial Microstructure

Abstract: Zirconia (ZrO₂) ceramic and Nb were brazed using Ag-Cu-Ti powder without and with Mo-particle-reinforced. The effects of the brazing temperature, holding time and Mo content of the composite filler on the interfacial microstructures and joining mechanism of ZrO₂/Nb brazed joints were investigated. By increasing the brazing temperature and holding time, the thickness of Ti₃Cu₃O layer increased and the thickness of TiO layer decreased, while the total thickness of the reaction layers increased slightly with the sufficient interfacial reaction. Meanwhile, the blocky Ti-Cu compounds gradually accumulate and grow up in the brazing seam. The calculated Ti activity increased first and then decreased as the Mo content was increased from 5 to 40 wt%. When the Mo content was 5wt%, only single Ti₃Cu₃O reaction layers formed adjacent to the ceramic substrate. By increasing of Mo particles, TiO layer became thicker. When 40 wt% Mo particles were added to the composite filler, Mo particles aggregated into larger clumps damaged the shear strength of brazing joint.

Abstract: The plates of 1Cr18Ni9Ti stainless steel were selected as metal substrates, and CrO₃+Al thermites were introduced into B₄C+Ti primary system for enhancing adiabatic temperature of reaction system. By improved processing route, i.e. respectively preparing, ball-milling and compacting B₄C+Ti blends and CrO₃+Al thermites and subsequently filling them one by one into the crucibles, TiB₂ ceramic to 1Cr18Ni9Ti graded composites were prepared by reaction joining in high-gravity field. it was found that refined TiB₂ platelets were embedded in or around the irregular TiC grains, and Fe-Cr-Ni metallic phases were distributed between TiC and TiB₂ phases, and Al₂O₃ inclusions disappeared completely at the intermediate between TiB₂ ceramic and 1Cr18Ni9Ti, the thickness of which reached 1.05 mm. The 3D net ceramic-metal composite microstructure (3DNCMCM) existed at the intermediate. The Vickers hardness distribution of the intermediate appeared the parabolic gradient composite feature, and the shear strength of the intermediate reached 325±15 MPa because of the increasing thickness of intermediate, at which 3D net ceramic-metal composite microstructure (3DNCMCM) existed.

Abstract: Continuous induction brazing with ultra-high frequency was proposed to braze the monocrystalline CBN grains using Ag-based filler alloy. The interfacial microstructure of the brazed specimen and the resultant morphology on the CBN surface was investigated and analogized by scanning electron microscopy (SEM) and energy diffraction X-ray (EDX). The experimental results showed that the bonding among CBN grains, filler alloy and steel matrix was achieved. The CBN grains were well wetted by the filler alloy and formed a massive support profile. Moreover, the active element Ti of the filler diffused markedly and gathered in the interfacial of matrix/filler and filler/grain respectively. Due to the short dwell time in brazing, the newly formed resultants grew in a short time. The resultants layer did not entirely covered the CBN grain, and discretely distributed on the surface of CBN grain. The size of the resultants was less than 200nm.

Abstract: Cu-Sn-Ti filler alloy was applied as brazing material to join UcBN grains onto the steel matrix using three different brazing temperatures (880, 900 and 920°C). The microstructure and properties of the UcBN-filler-steel joint and the compressive strength of UcBN grains were investigated respectively by means of scanning electron microscopy and energy dispersive X-ray spectroscopy and compressive test. The microstructural studies revealed an intermetallic interlayer of type TiN, TiB and TiB₂ at the joint interface, which grew with increasing brazing temperatures. The compressive force of UcBN grains with a maximum value of 79.3N was found when the brazing temperature was 900°C for 8 min. The wear process of brazed UcBN grains was a process transforming from abrasion wear to micro fracture mutually.

Abstract: The super brazed diamond saw was developed to cut efficiently vehicle tyre in the research. The carbon film deposited diamond and the uncoated diamond were brazed with NiCr alloy by high-frequency induction heating under argon atmosphere at 1030°C for 30 seconds respectively. The interfacial microstructures between the brazed diamond and the filler alloy were analyzed by the advanced testing technologies. The results shows that long-lath carbides with the definite orientation and better flatness are closely arrayed on the brazed uncoated diamond surface and Cr-carbides forms normally and compactly on the surface of carbon film deposited diamond brazed. That is because the carbon film has changed the mechanism of Cr-carbides forming on the surface of diamond brazed. The test of cutting vehicle tyre shows that the use life of the brazed deposited diamond saw is much longer than that of the brazed uncoated diamond saw.

Abstract: Self-lubrication CBN abrasive composite blocks and corresponding grinding wheels were made through the sintering process of CBN grains, graphite particles and Cu-Sn-Ti alloy at 920° for 30 min. The mechanical strength of the composite blocks was measured by means of the three-point bending experiments. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) were employed to characterize the fracture morphology and the interfacial microstructure of the composite blocks. Dressing experiments were carried out and the graphite film on the CBN grain surface was observed. The results obtained show that the bending strength of the composite blocks with 5 wt.% graphite particles reached 116 MPa, which met the mechanical requirements of the working layer of the grinding wheels. Chemical joining has taken place at the interface of CBN/Cu-Sn-Ti and graphite/Cu-Sn-Ti during the sintering process. Graphite film has been formed and spread to the grain surface after dressing.

Abstract: Abrasive composite bulks consisting of polycrystalline cubic boron nitride (PCBN) grains, Cu-Sn-Ti alloy and graphite particles were sintered at the heating temperature of 920 °C for the dwell time of 30 min. The bending strength of abrasive composite bulks was measured. The interfacial microstructure and the phases were characterized. In addition, the dressing experiment was carried out to detect the self-sharpening behavior of the composite bulks. Results obtained show that the abrasive composite bulks in this investigation give higher bending strength than that of the vitrified abrasive wheels. The compounds of TiN, TiB₂ were formed and the PCBN grains were embedded firmly. Strong fixing of the bulks to the PCBN grains led to the breakage of the PCBN grains when the abrasive composite bulks fractured. The intergranular fracture mode of the PCBN grains ensured the self-sharpening effect of the grains.

Abstract: The high performance diamond brazed saw was developed to cut efficiently AZ31 Magnesium Alloy. The Ti-coated diamond and the uncoated diamond were brazed with NiCr alloy by high-frequency induction under argon atmosphere at 1040°C within 20 seconds. Scanning electron microscopy (SEM), energy dispersion spectrometer (EDS) and X-ray diffraction (XRD) were used to investigate the interfacial microstructures between brazed diamond and the filler alloy. The results show that Cr-carbides forms normally and compactly on the surface of Ti-coated diamond brazed, whereas Cr-carbide forms tangentially and loosely on the surface of uncoated diamond brazed. That is because Ti has changed the mechanism of Cr-carbides formed on the surface of diamond brazed. The test of cutting AZ31 magnesium alloy plate shows that the section cut by Ti-coated diamond saw is much smoother than that cut by uncoated diamond saw after a long time.

Abstract: The interfacial microstructures and kinetics of low Ag content Sn2.5Ag0.7Cu/Cu solder joint were investigated by the X-ray diffraction, scanning electronic microscope and energy spectrum analysis during the isothermal aging. The results show that the interfacial microstructures of the Sn2.5Ag0.7Cu/Cu solder joint are composed of Cu₃Sn and Cu₆Sn₅ after soldering. With the aging time increasing, the intermetallic compound (IMC) pattern of the solder joint interface can be changed from the scallop-like to the shape-layer, and the growing dynamics is coincidence with the law of parabola and its growing behavior is controlled by diffusion. The growing activation energies values of Cu₃Sn and Cu₆Sn₅ layer at the Sn2.5Ag0.7Cu/Cu solder joint are 82.4kJ/mol and 69.6kJ/mol respectively.

Abstract: Mo₂FeB₂ Cermet Coating was deposited on Fe substrate by react flame spraying (RFS) process. Three different groups of specimens were prepared according to the change of induction heating treatment time. Comparative study of phase composition, microstructure, interfacial microstructure and bond strength of Mo₂FeB₂ Coating was carried out. X-ray diffractometry (XRD) and Scanning electron microscopy (SEM) were used to characterize the Mo₂FeB₂ coating. The bond strength between the coatings and Fe substrates was measured with the pull-off test method according to the corresponding GB 8642-88 standard. Results indicated that the time of induction heating treatment greatly affected the microstructure, interfacial microstructure and bond strength of Mo₂FeB₂ coating. 13 seconds of induction heating treatment favoured the formation of a compact Mo₂FeB₂ Coating with the highest bond strength of approximately 60 MPa.