Papers by Keyword: Dispersion Strengthening

Abstract: National Institute for Fusion Science (NIFS) launched in 2014 a research program for developing Dispersion Strengthened (DS) Cu alloys for application to the heat sink materials of divertors of fusion reactors, using newly installed ball-milling, encapsulation, and Hot Isostatic Pressing (HIP) facilities. A unique feature of these facilities is that the entire process can be performed without exposing the materials to air, enabling precise impurity control. Cu-Al, Cu-Zr and Cu-Y alloys have been produced in this program. Various technological advancement has been made for the fabrication, such as suppression of powder adhesion to the wall of containers during the ball milling, and encapsulation technology including development of small volume tubular capsules.

Abstract: The enhanced dispersion strengthening of Sm in Mg-10Y-0.5Sm has been investigated by means of microstructure analysis and tensile tests. The results show that Sm addition improves the image of Mg₂₄Y₅ phase and causes the formation of fine and dispersed Mg₂₄Y₅ phase. Meanwhile, the dissolved Sm increases the thermal stability of Mg₂₄Y₅ phase and enhances its dispersion strengthening in the alloy. It leads to the increased tensile strength of the alloy at elevated temperatures.

Abstract: Using high energy ball milling method through changing the content (mass fraction) of alumina to sinter alumina particle dispersion reinforced copper matrix composites with different Al2O3 contents. The effects of alumina content on the microstructure and properties of the sintered body were studied by microstructure observation, relative density, electrical resistivity and hardness test. The results show that when the milling speed was 1400r/min, with the increase of the content of alumina, the relative density decreased, the electrical resistivity increased, the hardness increased first and then decreased. When the Al2O3 content was 1wt% the maximal relative density was 96.4% and the lowest electrical resistivity was 30.843 nΩ•m.

Abstract: This study had been carried out to investigate the effect of micron size Ni particle addition on the microstructure, melting behavior and mechanical properties of the ternary Sn-9Zn solder alloys. Different weight percentage, viz. 0.25, 0.5 and 1 of micron size Ni particle was added in the liquid Sn-9Zn alloy and then cast into the metal mold. Melting behavior was studied by Differential Thermal Analyzer (DTA). Microstructural investigation was conducted using Optical and Scanning Electron Microscope (SEM). Tensile properties were determined at a strain rate 3.00 mm.min-1. The results indicated that Ni addition increased both the melting point and solidification range of the Sn-9Zn solder alloy. The microstructures of newly developed ternary Sn-9Zn-xNi solder alloys consisted of fine needle-like α-Zn phase dispersed in the β-Sn matrix. It was found that small amount of Ni (0.25 wt. %) addition refined and dispersed the Zn needles throughout the matrix. Besides, enhanced precipitation of Zn in the β-Sn matrix was also observed. All these structural changes increased the hardness and tensile strength of Sn-9Zn alloy with the addition of Ni particle to a certain amount.

Abstract: Structural changes in a 9%Cr martensitic steel after 1%, 4% creep and creep rupture test at 650°C and stress of 118 MPa were examined. Heat treatment provided the formation of tempered martensite lath structure (TMLS) in the steel. The precipitations of second phase particles along block and lath boundaries provide effective stabilization of the TMSL under annealing/aging condition. This structure hardly changed under creep conditions in grip portion of crept sample. Significant coarsening of both the second phase particles and the martensite laths takes place in neck portion. In addition, the latter ones lose their original morphology and are replaced by large strain-induced subgrains. It should be noted that the increase of subgrain size is in almost direct proportion to the particle growth during the creep to 4% strain. The rapid growth of martesite laths followed by their evolution to deformation subgrains takes place within the tertiary creep regime.

Abstract: The Zener drag force exerted by M₂₃C₆ carbides, Fe₂(W,Mo) Laves phase and M(C,N) particles for migration of different grain boundaries in P92-type and P911+3%Co heat-resistant steels was calculated. In particular, the prior austenite grain boundaries (PAGB), boundaries of packets and blocks, which are mainly high-angle boundaries (HAGB), were addressed. Zener pinning pressures were determined for each type of dispersoids separately taking into account that the M₂₃C₆ carbides, Fe₂(W,Mo) Laves phase are inhomogeneously distributed such that they are mainly located at the boundaries, and the M(C,N) dispersoids are uniformly distributed throughout the metallic matrix. In the both steels, the pinning pressure from the second phase particles located at grain boundaries is about an order of magnitude higher than that caused by homogeneously distributed MX precipitates. In spite of numerous second phase particles precipitated during tempering, grain growth (although rather moderate) occurred during the creep tests of the studied materials. The driving pressure for grain boundary motion might be mostly associated with high dislocation density retained in the tempered martensite structure. The resulting pressure for grain growth in the P92-type steel under creep conditions at 600 and 650°C is somewhat higher than that for the P911 steel.

Abstract: In order to develop new electrical contact materials with better properties, small amounts of rare earth (RE) oxides were selected as additions into AgSnO2-based composites. The effects of different RE oxide additions with different content in the matrix on the microstructure of AgSnO2, were investigated. In general, the resulting RE oxide-doped materials are found to have better performances than their original ones. Results indicate that the newly developed AgSnO2/La2O3 materials in this paper are leading candidates for environmentally friendly electrical devices and RE oxides would play an important role in improving performance of AgSnO2.

Abstract: The tempered microstructure and the creep behaviour were studied in an ultra low carbon 9%Cr martensitic creep resistant steel. The starting material was forged at 1050°C followed by air cooling and then tempered at a temperature of 750°C for 3 hours. This treatment resulted in the mean transverse lath size of about 240 nm; the dislocation density in lath interiors comprised 4 × 10¹⁴ m^-2. The tempered martensite lath structure (TMLS) is characterised by homogeneous precipitation of numerous MX-type carbonitrides and a small amount of relatively coarse M₂₃C₆–type carbides. Three kinds of MX carbonitrides were observed in the tempered lath martensite structure. Those were plate-shaped particles with longitudinal size of about 15 nm and thickness of 3 nm; round-shaped particles of about 10 nm in diameter; and relatively large almost equiaxed particles with mean size of about 90 nm. The large MX particles were resulted from incomplete dissolution of such carbonitrides at 1050°C, while the nanoscale particles homogeneously precipitated during the tempering. The creep tests conducted at 650°C showed that the studied steel demonstrated superior creep resistance. Namely, the rupture time was about an order as long as that for P92-type creep resistant steel.

Abstract: The nano Al₂O₃ -Cu/Cr composite was prepared by a simplified internal oxidation technique of the vacuum hot-press sintering-internal oxidizing method. The tensile strength and microhardness were determined respectively. The microstructures were analyzed by means of a scanning electron microscope (SEM). On the basis of above results, the main strengthening mechanisms were investigated by quantitative calculation of several strengthening effects. The experimental results show that the microhardness and tensile strength obviously increase with increased cold deformation. The main strengthening mechanisms of the nano Al₂O₃ -Cu/Cr composites are mainly attributed to the dispersion of the nano-scale of alumina particles and the aggregate of the Cr particle phase, of which the former can restrict the mobility of the dislocations and increase the density of dislocations. Meanwhile, the cold deformation strengthening has some important effect to a certain extent.

Abstract: By alloying principle, a novel quaternary high-temperature lead-free solder was formed by adding trace Sn into Bi5Sb2Cu. The influences of trace Sn on the microstructure and mechanical properties of the novel solder alloy were systematically investigated. Results show that the new phases â-SnSb and mesh Sb2Sn3 are formed and dispersed in the novel solder, whose dispersion strengthening make the tensile strength and shear strength of the new solder alloy increase. When Sn is less than 8 wt%, the tensile strength and the shear strength of the new solder increase with the increasing of content of Sn. When Sn is 8wt%, the tensile strength and shear strength is respectively 52.79MPa and 17.00MPa, which is respectively improved about 90.6% and 64 wt.% compared to the matrix solder. When Sn is 10wt.%, the mechanical properties of the solder take a decrease trend, but they are still better than those of the matrix solder.