钨板加工技术的现状与发展

介绍了钨板材加工技术的现状和发展趋势。粉冶法已成为工业规模生产钨锭的主要方法;轧制开坯成为粉冶法钨锭的主要开坯工艺;深加工技术是把板材转变成元件、部件,甚至是设备的关键技术。发展净化技术,实施精品战略,高技术不断渗入钨板材加工技术已成为钨板加工技术的重要发展趋势。

Age-hardening behavior and microstructure of Cu-15Ni-8Sn-0.3Nb alloy prepared by powder metallurgy and hot extrusion

Cu-15Ni-8Sn-0.3Nb alloy rods were prepared by means of powder metallurgy followed by hot extrusion.Element maps obtained by electron probe micro analyzer(EPMA)showed that Nb-rich phases were formed and distributed within grains and at grain boundaries of the Cu-15Ni-8Sn-0.3Nb alloy.Transmission electron microscope(TEM)results indicated that there was no obvious orientation relationship between these phases and the matrix.Spinodal decomposition and ordering transformation appeared at early stages of aging at400°C and caused significant strengthening.Cu-15Ni-8Sn-0.3Nb alloy exhibited both higher strength(ultimate tensile strength>1030MPa)and higher tensile ductility(elongation>9.1%)than Cu-15Ni-8Sn alloy after aging treatment.The improvement was caused by Nb-rich phases at grain boundaries which led o the refinement of grain size and postponed the growth of discontinuous precipitates during aging.

Microstructural evolution in a powder metallurgical Ti-7Mo alloy with continuous oxygen gradient

A titanium alloy containing continuous oxygen gradient was prepared by powder metallurgy(P/M) and the composition–property relationship was studied on a single sample. The alloy was sintered with layered powder of different oxygen contents via vacuum sintering and spark plasma sintering(SPS), respectively. After subsequent heat treatments, high-throughput characterizations of the microstructures and mechanical properties by localized measurements were conducted. The Ti-7% Mo(molar fraction) alloy with an oxygen content ranging from 1.3×10^(-3) to 6.2×10^(-5)(mass fraction) was obtained, and the effects of oxygen on the microstructural evolution and mechanical properties were studied. The results show that SPS is an effective way for fabricating fully dense Ti alloy with a compositional gradient. The average width of α′ phase coarsens with the increase of the content of oxygen. The content of α″ martensitic phase also increases with the content of oxygen. At oxygen contents of 3×10^(-3) and 4×10^(-3)(mass fraction), the Ti alloys present the lowest microhardness and the lowest elastic modulus, respectively. The results also indicate that the martensitic phases actually decrease the hardness of Ti-7Mo alloy, and oxygen effectively hardens the alloy by solid solution strengthening. Therefore, the high-throughput characterization on a microstructure with a gradient content of oxygen is an effective method for rapidly evaluating the composition–property relationship of titanium alloys.

Statistical evaluation and optimization of zinc electrolyte hot purification process by Taguchi method

The neutral zinc sulfate solution obtained from hydrometallurgical process of Angouran zinc concentrate has cadmium, nickel and cobalt impurities, that must be purified before electrowinning. Therefore, cadmium and nickel are usually cemented out by addition of zinc dust and remained nickel and cobalt cemented out at second stage with zinc powder and arsenic trioxide. In this research, a new approach is described for determination of effective parameters and optimization of zinc electrolyte hot purification process using statistical design of experiments. The Taguchi method based on orthogonal array design（OAD） has been used to arrange the experimental runs. The experimental conditions involved in the work are as follows： the temperature range of 70-90 ℃ for reaction temperature（T）, 30-90 min for reaction time（t）, 2-4 g/L for zinc powder mass concentration（M）, one to five series for zinc dust particle size distributions（S1-S5）, and 0.1-0.5 g/L（C） for arsenic trioxide mass concentration. Optimum conditions for hot purification obtained in this work are T4（85 ℃）, t4=75 min, M4=3.5 g/L, S4（Serie 4）, and C2=0.2 g/L.

Synthesis of Al-SrB_6 composite via powder metallurgy processing

The potential of powder metallurgy processing for the manufacture of Al?SrB6 composites was explored. Al4Sr particles fractured extensively during the ball milling of Al?15Sr/Al?4B powder mixtures. There was no interaction between the Al4Sr and AlB2 compounds across the section of the aluminium grains in the as-milled state. SrB6 formed, when the ball milled powder blends were subsequently annealed at sufficiently high temperatures. Ball milling for 1 h was sufficient for SrB6 to become the major constituent in powder blends annealed at 700 °C while it took 2 h of ball milling for powder blends annealed at 600 °C. Higher annealing temperatures and longer ball milling time encouraged the formation of the SrB6 compound while the latter made a great impact on the microstructural features of the Al?SrB6 composite. The SrB6 compound particles were much smaller and more uniformly distributed across the aluminium matrix grains in powder grains ball milled for 2 h before the annealing treatments at 600 °C and 700 °C.

Key parameters for low temperature warm compaction of high density iron-based P/M materials

In order to reduce powder temperature to lower than 100℃ in warm compaction by changing polymer lubricant design, powder flowability, warm compacting behavior, lubricating mode as well as ultimate tensile strength after sinter-hardening and tempering were investigated systematically. By means of low temperature warm pressing and sintered hardening technique, samples with the sintered densities of 7.407.45g/cm3 and the strengths of 950 1390MPa are achieved as the early compacting pressure is 686735MPa.

Parametric optimization of dry sliding wear loss of copper-MWCNT composites

The wear behavior of multi-walled carbon nano-tubes(MWCNTs)reinforced copper metal matrix composites(MMCs)processed through powder metallurgy(PM)route was focused on and further investigated for varying MWCNT quantity viaexperimental,statistical and artificial neural network(ANN)techniques.Microhardness increases with increment in MWCNTquantity.Wear loss against varying load and sliding distance was analyzed as per L16orthogonal array using a pin-on-disctribometer.Process parameter optimization by Taguchi’s method revealed that wear loss was affected to a greater extent by theintroduction of MWCNT;this wear resistant property of newer composite was further analyzed and confirmed through analysis ofvariance(ANOVA).MWCNT content(76.48%)is the most influencing factor on wear loss followed by applied load(12.18%)andsliding distance(9.91%).ANN model simulations for varying hidden nodes were tried out and the model yielding lower MAE valuewith3-7-1network topology is identified to be reliable.ANN model predictions with R value of99.5%which highly correlated withthe outcomes of ANOVA were successfully employed to investigate individual parameter’s effect on wear loss of Cu?MWCNTMMCs.

Porous Ti-10Mo alloy fabricated by powder metallurgy for promoting bone regeneration

Porous Ti-lOMo alloys were fabricated by powder metallurgy using a space-holder method. The pore characteristics, m icrostructure, mechanical properties, in vitro biocompatibility, and in vivo osseointegration of the fabricated alloys were systematically investigated. The results show that with different weight ratios of the space-holder (NH4- HC03) added, all of the porous Ti-10Mo alloys sintered at 1,300℃ exhibited a typical W idmanstatten microstructure. The porosity and average pore size of the porous structures can be controlled in the range of 50.8%-66.9% and 70.1 -381.4μm , respectively. The Ti-10Mo alloy with 63.4% porosity exhibited the most suitable mechanical properties for implant applications with an elastic modulus of 2.9 GPa and a compressive yield strength of 127.5 MPa. In vitro9 the alloyconditioned medium showed no deleterious effect on the cell proliferation. The cell viability in this medium was higher than that of the reference group, suggesting non-toxicity and good biological characteristics of the alloy specimens. In vivo, after eight weeks* implantation, new bone tissue formed surrounding the alloy implants, and no noticeable inflammation was observed at the implantation site. The bone bonding strength of the porous Ti-10Mo alloy increased over time from 46.6N at two weeks to 176.4 N at eight weeks. Suitable mechanical properties together with excellent biocompatibility in vitro and osteointegration in vivo make the porous Ti-10Mo fabricated by powder metallurgy an attractive orthopedic implant alloy.