新型高强韧性冷作模具钢DM9的组织和性能

研究了新型模具钢DM9（含量范围％：0．83－0．95C，3．5－4．2Cr，1．9－2．5W，0．8－1．2Mo，0．7－1．1Si，0．35－0．55V）的组织和性能。试验结果表明，该钢DM9在840℃退火时存在M3C，M23C6，M6C，M7C3和MC5种类型碳化物，碳化物平均尺寸0．66μm；该钢950℃淬火220℃回火后，硬度HRC62，抗弯强度σbb3800MPa，冲击韧度ak72J/cm^2，其模具有高的寿命。     

Thermal stability of primary carbides and carbonitrides in two cast Ni-base superalloys

Thermal stability of primary MC carbide and M(CN) carbonitride in K452 and K446 alloys is investigated. In K452 alloy, primary MC is very unstable relative to M(CN) for the former contains a higher content of the weakeners (W and Mo) than the latter. The ratios of element contents (at.%) (W + Mo)/Cr, (W + Mo)/(Ti + Nb) and Nb/Ti are three important parameters, which together determine the thermal stability of primary MC. Also, primary MC degeneration plays an important role in the microstructural instability of K452 and K446 alloys.     

Wear Behaviour and Tool Life of Wire-EDM-ed and Ground Carbide Punches

This paper describes and discusses the wear behaviour and tool life of a cemented carbide punch produced in eight different qualities. Six samples covering a wide variety of EDM surface textures and surface integrities are compared to the performance of two ground punches. All punches have been tested on an industrial press. Burr height measurements on the stamped material, used as an evaluation of tool life, does not indicate significant influences of the production process. A more detailed analysis of the punch surface after 1×10⁶ punch cycles shows the presence of different wear zones. The surface layer influenced by the production process, either EDM or grinding, is completely removed in the zones near the cutting edge.     

Determination of the eutectic solubility lines of the ternary system NaHCO3–Na2CO3–H2O

A crystallizer was built and a procedure developed to accurately measure the eutectic solubility lines where ice and salt coexist in equilibrium with the solution, for potential application of Eutectic Freeze Crystallization. The eutectic solubility lines of the ternary system NaHCO₃–Na₂CO₃–H₂O were determined experimentally and calculated with the extended UNIQUAC model. The extended UNIQUAC model describes the experimental data quite well. Anhydrous NaHCO₃ and Na₂CO₃·10H₂O were the only two types of crystals present in equilibrium with ice crystals in the ternary system. At the quadruple point NaHCO₃ and Na₂CO₃·10H₂O are in equilibrium with a solution of about 4.34 wt% of Na₂CO₃ and 4.77 wt% of NaHCO₃ at −3.32 °C. The anhydrous NaHCO₃ crystals were needle shaped with lengths between 5 and 10 μm, that were agglomerated into particles of about 100–300 μm, while the Na₂CO₃·10H₂O crystals were hexagonally shaped with sizes between 100 and 500 μm.     

Design of a Eutectic Freeze Crystallization process for multicomponent waste water stream

Complex, hypersaline brines originating from the mining and extractive metallurgical industries have the potential to be treated using Eutectic Freeze Crystallization (EFC). Although EFC has been shown to be effective in separating a single salt and water, it has yet to be applied to the complex hypersaline brines that are typical of reverse osmosis retentates in South Africa. This paper focuses on the application of EFC for the purification of a typical brine containing high levels of sodium, chlorine, sulphate and ammonia that cannot be achieved with other separation techniques. The presence of ammonia prevents the application of membrane technology to treat the brine, leaving only cooling or evaporation as other possible options. Evaporation produces a mixed salt that requires further treatment. Modelling tools were applied to describe the phase behaviour of the complex saline systems under different process conditions and were experimentally validated. The results showed that Eutectic Freeze Crystallization could be used to selectively recover the sodium as a sodium sulphate salt. The simulation tools were especially useful in the design and optimisation of the process.     

Microstructure, growth mechanism and mechanical property of Al2O3-based eutectic ceramic in situ composites

Directionally solidified Al₂O₃-based eutectic ceramic in situ composites with inherently high melting point, low density, excellent microstructure stability, outstanding resistance to creep, corrosion and oxidation at elevated temperature, have attracted significant interest as promising candidate for high-temperature application. This paper reviews the recent research progress on Al₂O₃-based eutectic ceramic in situ composites in State Key Laboratory of Solidification Processing. Al₂O₃/YAG binary eutectic and Al₂O₃/YAG/ZrO₂ ternary eutectic ceramics are prepared by laser zone melting, electron beam floating zone melting and laser direct forming, respectively. The processing control, solidification characteristic, microstructure evolution, eutectic growth mechanism, phase interface structure, mechanical property and toughening mechanism are investigated. The high thermal gradient and cooling rate during solidification lead to the refined microstructure with minimum eutectic spacing of 100 nm. Besides the typical faceted/faceted eutectic growth manner, the faceted to non-faceted growth transition is found. The room-temperature hardness H_V and fracture toughness K_IC are measured with micro-indentation method. For Al₂O₃/YAG/ZrO₂, K_IC = 8.0 ± 2.0 MPa m^1/2 while for Al₂O₃/YAG, K_IC = 3.6 ± 0.4 MPa m^1/2. It is expectable that directionally solidified Al₂O₃-based eutectic ceramics are approaching practical application with the advancement of processing theory, technique and apparatus.     

碳化钨、钨及其复合物料中痕量砷的测定

对碳化钨样品中的痕量砷进行了分析测定,试样以硝酸、氢氟酸低温溶解,硫—磷混酸冒烟驱除硝酸和氢氟酸,用预还原剂还原高价砷(Ⅴ)为低价砷(Ⅲ),进行氢化物原子吸收光谱测定,测得结果与摄谱法及分光光度法结果一致。     

单键拉刀早期断裂分析

对断裂单键拉刀进行了化学成分分析、硬度测定和金相检验，严重的碳化物带状偏析，使拉刀产生局部淬火过烽回火不足，造成内应力急剧增高，最终导致拉刀断裂。     

Impact toughness in Al–12Si and Al–12Si–3Cu cast alloys—Part 1: Effect of process variables and microstructure

The charpy impact energy of Al–12Si and Al–12Si–3Cu cast alloys was measured in terms of the total absorbed energy. The standard charpy specimens 10×10×55 mm with a 2 mm V-notch were prepared from the castings. Effect of process variables and microstructural changes on the impact toughness of Al–12Si and Al–12Si–3Cu cast alloys was investigated. The results indicate that combined grain refined and modified Al–12Si–3Cu cast alloys have microstructures consisting of uniformly distributed α-Al dendrites, eutectic Al–Si and fine CuAl₂ particles in the interdendritic region. These alloys exhibited better impact toughness in the cast condition compared with the same alloy subjected to only grain refinement or modification.     

Microstructure and Eutectic Carbide Morphology of the High Speed Steel Strips Produced by Twin Roll Strip Casting Process

The M2 high-speed steel strip was produced by using the laboratory scale twin roll strip caster. The microstructure and eutectic carbide morphology of thus produced products were observed and analyzed, and the comparison of those with conventional products was carried out. The effects of the processing parameters such as the melting temperature, the pouring temperature, rolling speed and separating force on the microstructure and eutectic carbide morphology and their distribution were analyzed. The spheroidizing process of the strips in the annealing process was investigated. The relations between the growth and spheroidizing of the eutectic carbide and the annealing technology were obtained, and the mechanism of the twin roll strip casting process improving the eutectic carbide spheroidizing was discussed. The theoretical instruction for determining the subsequent treatment process was provided.