B2结构Fe3Al单晶室温力学行为各向异性的研究

研究了Ｂ２结构Ｆｅ３Ａｌ单晶室温下的力学行要现,依取向不同。材料的屈服强度,延伸率,加工硬化率存在很大差异,近「１１０」取向具有最高延伸率为４２％,而近「１００」取向只获得了１４．１％的延伸率,近「１１０」取人有的高加工硬化率是位错交互作用的结果。二分位错分解为单根位错导致交滑移。进一步提高高延伸率近「２１１」取向的低加工硬化率是单系滑移的结果。在此取向下直至断裂,样品中仍为二分位错。     

A high-temperature oxidation-resistant Fe-Mn-Al-Si alloy

To develop satisfactory alloys without Cr or Ni for high-temperature application up to 1100C, three alloys based on Fe-10%Al-Si with differing fourth (or fifth) element additions were oxidized in air at 1100°Cfor 24 hr. A low carbon, Fe-30Mn-10Al-Si alloy exhibited excellent high-temperature oxidation resistance. The total weight gain for 24 hr oxidation in air at 1100°C was only 1.03 mg/cm ². After air oxidation for 6 days at 1100°C, no nodule formation or breakthrough oxidation occurred. Post-oxidation SEM and EDAX examination showed that a thin, compact, protective alumina scale formed on the alloy.Visiting Scientist (People's Republic of China).     

Microstructure control and high temperature properties of TiAl base alloys

An equiaxed fine grain structure, a γ grain structure with the precipitated ₂ laths, and a fully lamellar structure were obtained by the microstructure control using thermomechanical processing and heat treatment. The key to obtaining the equiaxed fine grain structure using isothermal forging is to decompose the lamellar structure and then produce the fine grain microstructure through dynamic recrystallization. TiAl base alloys consisting of fine equiaxed grains, in particular, Ti-39Al-9V consisting of the γ and B2 phases exhibited superplastic elongation of more than 600% at 1423 K. Creep rupture properties of TiAl binary alloys with various microstructures were studied in purified He in the temperature range from 1073 to 1373 K. Above 1173 K the precipitated ₂ phase improved the steady state creep rate and creep life. At 1023 K, the ₂ phase did not improve the creep rate, although the steady state creep rate decreased and the creep life increased as the γ grain size increased.     

Wear resistance properties of austempered ductile iron

A detailed review of wear resistance properties of austempered ductile iron (ADI) was undertaken to examine the potential applications of this material for wear parts, as an alternative to steels, alloyed and white irons, bronzes, and other competitive materials. Two modes of wear were studied: adhesive (frictional) dry sliding and abrasive wear. In the rotating dry sliding tests, wear behavior of the base material (a stationary block) was considered in relationship to countersurface (steel shaft) wear. In this wear mode, the wear rate of ADI was only one-fourth that of pearlitic ductile iron (DI) grade 100-70-03; the wear rates of aluminum bronze and leaded-tin bronze, respectively, were 3.7 and 3.3 times greater than that of ADI. Only quenched DI with a fully martensitic matrix slightly outperformed ADI. No significant difference was observed in the wear of steel shafts running against ADI and quenched DI. The excellent wear performance of ADI and its countersurface, combined with their relatively low friction coefficient, indicate potential for dry sliding wear applications. In the abrasive wear mode, the wear rate of ADI was comparable to that of alloyed hardened AISI 4340 steel, and approximately one-half that of hardened medium-carbon AISI 1050 steel and of white and alloyed cast irons. The excellent wear resistance of ADI may be attributed to the strain-affected transformation of high-carbon austenite to martensite that takes place in the surface layer during the wear tests.     

次亚磷酸钠对贮氢合金活化性能的影响

采用次亚磷酸钠溶液对熔体旋淬技术制备的快凝贮氢合金粉ＭｌＮｉ３．６Ｃｏ０．７Ｍｎ０．３Ａｌ０．４进行还原处理,使其表面形成一个富Ｎｉ层,可显著改善合金粉的电化学活性．经处理的快淬合金粉仅２次充放电循环其放电容量便可达到２４１ｍＡ·ｈ·ｇ－１,而未经处理的同一合金粉经５次充放电循环其放电容量也只有２２２ｍＡ·ｈ·ｇ－１．ＡＥＳ及ＸＰＳ分析表明表面氧化层的性质对于在碱溶液中金属氢化物电极的活化过程具有重要影响．     

Thermal behavior of B_4C particles under plasma arc powder surfacing condition

0InstructionCarbides.asavariesofadvancedcoatingmaterialsfortheirsuperhardnessandexcellentthenllalstabilizer,havebeenwidelyusedinplasmaspra}illgandlasercladdingprocess.andattractedmuchattentionl"ZI.Especially.theresearchpapersaboutmetalcarbidessuchasTiC.WC…     

MIM Fe基合金的合金化强化

研究金属粉末注射成形铁基合金在强还原性氢气氛烧结条件下的合金化强化效果，结果表明，添加Ｃｕ、Ｎｉ、Ｍｏ等元素能取得显著的固溶强化效果，其中成分为Ｆｅ－２Ｎｉ－２Ｃｕ－０．４５Ｍｏ的机械性能达到σｂ＝４８３ＭＰａ，σｓ＝３４０ＭＰａ，δ＝９％和ＨＲＢ８３。     

Effects of porous carbon on sintered Al-Si-Mg matrix composites

The influence of microporous particulate carbon char on the mechanical, thermal, and tribological properties of wear-resistant Al-13.5Si-2.5Mg alloy composites was studied. Large increases in surface area due to the formation of micropores in coconut shell chars were achieved by high-temperature activation under CO₂ gas flow. Activated char particles at 0.02 V _f were used to reinforce the alloy. The composites were fabricated via a double-compaction reaction sintering technique under vacuum at a compaction pressure of 250 MPa and sintering temperature of 600 °C. At more than 35% burn-off of the carbon chars at the temperature of activation, 915 °C, the total surface area remained virtually unaffected. The ultimate tensile strength and hardness decreased by 23% and 6 %, respectively; with increasing surface area of the reinforcement from 123 to 821 m²g⁻¹. The yield strength and the percentage of elongation decreased by a factor of 2 and 5, respectively. No significant change in sliding wear rate was observed but the coefficient of friction increased by 13 % (0.61 to 0.69). The coefficient of linear thermal expansion was reduced by 16 % (11.7 × 10⁻⁶ to 9.8 × 10⁻⁶ °C⁻¹), and remained unaffected at more than 35 % burn-off. Energy-dispersive spectrometry of the particles of the activated chars showed that oxides of potassium and copper coated the open surfaces. Failure at the matrix-char interface was observed, and this was attributed to localized presence of oxides at the interfaces as identified by electron probe microanalysis. Poor wetting of the oxides by magnesium at the sintering conditions resulted in formation of weak matrix-char interface bonds. J.U. Ejiofor, formerly of the Department of Metallurgical and Materials Engineering, The University of Alabama     

铸钢件准固态区域应力,应变数值模拟及热裂机制

对ＺＧ４５实验热裂试棒的数种工况进行了应力－应变的数值模拟，对热裂形成机制进行了讨论。研究认为：热裂起源于Ｂｉｎｇｈａｍ体，是塑性变形超过Ｂｉｎｇｈａｍ体塑性储备值所致。     

Corrosion of nickel-base and iron-base alloys in a simulated fluidized-bed coal-combustion environment

The modes of initiation and propagation of corrosion attack on a series of high-temperature alloys were studied in synthetic gas mixtures at 900°C. The gas mixtures were intended to simulate the oxygen and sulfur partial pressures experienced in reducing zones in a coal-fired fluidized-bed combustor and comprised mixtures of CO, CO₂, and SO₂. The alloys studied were candidates for in-bed heat exchanger tubing for an air-heater cycle operating at 843°C and 300–500 psig and so ranged from type 300-series stainless steels to nickel-base alloys. With the exception of two FeCrAlY alloys and types 304 and 347 stainless steels, it was found that sulfidation corrosion could be initiated on all the alloys within 0.25 hr; the rate of propagation of the corrosive attack depended on the flux of SO₂ in the environment and on the nickel content of the alloys. The presence of iron in the alloys appeared to slow the initiation of sulfidation, by forming a continuous iron oxide layer. The effects of various alloying additions are discussed, and a schematic model for the initiation of sulfidation is proposed.