Effects of pressing temperature on the consolidation of titanium nickelide powders

The plastic aftereffect and the shape memory effect hinder the manufacture of high-density materials based on titanium nickelide by traditional powder metallurgy methods. Studies have been made on the effects of temperature and pressing pressure for powders containing titanium nickelide on the elastic aftereffect, crystal growth during the initial stage of sintering, and density of the sintered material. If the pressing is at a temperature exceeding the temperature for the start of the martensite transformation, one can increase the density of the material substantially by comparison with pressing at room temperature. For that purpose, the pressing temperature needs to be raised only to 200°C.Tomsk Polytechnical Institute. Translated from Poroshkovaya Metallurgiya, No.3 (363), pp. 19–22, March, 1993.     

含锰磁铁矿球团氧化固结机理分析

为促进含锰磁铁矿在球团上的应用,通过造球试验,并借助X射线衍射和扫描电子显微镜等检测手段,系统地分析了Mn₃O₄对球团矿氧化固结机理的影响。结果表明,随着Mn₃O₄质量分数从0%增加至7%,球团抗压强度从2 458 N/个降到1 810 N/个,孔隙率从22.7%增大至26.2%。随着Mn₃O₄的增加,在赤铁矿晶界和硅酸盐相中形成新的MnFe₂O₄固熔体,固熔体扩大了基体中的裂纹,破坏了赤铁矿的连续结晶;硅酸盐含量增加也极大地抑制了赤铁矿晶粒的生长,使含锰球团的基体由致密变为多孔,球团矿强度降低。故对生产企业来说,Mn₃O₄对球团的固结强化有负面影响,其适宜的质量分数应在3%以内。     

含锰磁铁矿球团氧化固结机理分析

为促进含锰磁铁矿在球团上的应用,通过造球试验,并借助X射线衍射和扫描电子显微镜等检测手段,系统地分析了Mn₃O₄对球团矿氧化固结机理的影响。结果表明,随着Mn₃O₄质量分数从0%增加至7%,球团抗压强度从2 458 N/个降到1 810 N/个,孔隙率从22.7%增大至26.2%。随着Mn₃O₄的增加,在赤铁矿晶界和硅酸盐相中形成新的MnFe₂O₄固熔体,固熔体扩大了基体中的裂纹,破坏了赤铁矿的连续结晶;硅酸盐含量增加也极大地抑制了赤铁矿晶粒的生长,使含锰球团的基体由致密变为多孔,球团矿强度降低。故对生产企业来说,Mn₃O₄对球团的固结强化有负面影响,其适宜的质量分数应在3%以内。     

温度对GH4169合金蠕变行为及机制的影响

在研究了温度对镍基高温合金GH4169蠕变行为及机制的影响基础之上,分析了其断口形貌和蠕变断裂机理。实验结果表明,随着蠕变温度的升高,GH4169合金的稳态蠕变速率逐渐升高,蠕变寿命显著降低,即该合金有极强的温度敏感性。蠕变过程中,γ″相长大聚集,并向δ相转变,随着蠕变温度的升高,γ″相向δ相转变速度加快,晶内的γ″相数量减少,δ相所占体积增加,尺寸增大,次生裂纹数量减少,尺寸减小。当蠕变温度为650 ℃时,断口中存在较多亮白色撕裂棱,韧窝尺寸大小不一,有少量析出物和碳化物;当温度提高到670 ℃时,韧窝尺寸减小,以浅韧窝为主,且出现解理面;当温度提高到690 ℃时,只存在少量韧窝,且δ相的数量显著增多,出现解理台阶,断裂方式为解理断裂或准解理断裂。      

赤铁矿内配兰炭生产球团矿固结机制研究

通过对不同温度、不同兰炭配入量的内配兰炭赤铁矿球团进行FeO含量检测和矿相结构分析,得出兰炭在赤铁矿球团焙烧过程中的作用机制.结果表明:兰炭含量较低时,主要发生燃烧反应,不利于赤铁矿向磁铁矿转变,且气孔率增大使球团抗压强度降低;兰炭含量过高,还原反应占主导,大量Fe2O3被还原为Fe3O4,甚至被还原为FeO,随之形成...     

Effect of the quenching temperature on the structure and deformation mechanism of a VT22I alloy

The effect of the temperature of heating for quenching on the phase composition, structure, and deformability of a high-strength VT22I titanium alloy is studied. After quenching from a critical temperature or above, an unstable β phase forms in the structure of the alloy; upon further deformation up to 3%, this phase transforms into the α” martensite. This process occurs at low stresses (150–200 MPa) and is characterized by an increase in the internal friction of the material, which is related to the high mobility of interfacial and twin boundaries of β-phase and martensite crystals. In VT22I alloy samples quenched from below the critical temperature, a mechanically stable β phase forms; it is deformed according to a slip mechanism at sufficiently high stresses (550 MPa).     

Effect of cyclic pressure consolidation on the uniformity of metal matrix composites

The cold compaction of ceramic-metal powder blends by the cyclic application of pressure improves compacted density. This enhanced densification has been attributed to a repeated generation of mismatch strain between the matrix and reinforcement phases, in a process similar to that seen in the thermal cycling of fully dense composites. It was postulated that cyclic compression may also reduce density gradients and improve overall uniformity. To test this hypothesis, aluminum and alumina powders were mixed and consolidated under both monotonic and cyclic loading at room temperature. Three aspect ratios were used and double-action compaction was included. X-ray computed tomography (CT) shows that the spatial density of uniformity improved during cyclic compaction. The distribution of ceramic particles was found to be more uniform following pressure cycling, especially for compacts having lower aspect ratios. A composite with 40 pct reinforcement achieved nearly uniform full density following double-action cyclic compaction. Cyclic compaction improves overall density as well as density uniformity and reinforcement distribution uniformity.     

Effect of particle composition on consolidation of hot briquetted iron

Abstract

The influence of the carbon concentration of directly reduced iron (DRI) powders on the compressibility and fracture strength of hot briquetted iron (HBI) has been studied. Industrially produced DRI, pure iron powder and Fe–C alloy powders (synthetic DRI) were used in the study. It was found that the mechanism of compaction could be attributed to pure yielding. The pressure required to attain a given density increased proportionally with the carbon content. The morphology and phases present in DRI powder had a significant influence on the compressibility. The fracture strength of the compacts increased with increasing carbon content of the DRI powder. These observations are discussed with reference to the current understanding of the mechanisms of compaction and fracture of compacted particulate materials.     

Al-Ni-Y合金雾化粉末的超高压固结成形及其机理研究

采用紧耦合惰性气体雾化技术制备具有非晶和纳米晶结构的Al82Ni10Y8(%)合金粉末, 粒径小于26μm粉末为非晶和纳米晶结构, 而粒径小于15μm粉末为非晶单相结构。在250, 310, 360, 400, 450℃5个不同温度下对粉末进行了超高压固结成形, 并对致密化后合金的显微结构进行了分析。致密化后粉末颗粒基本保持原有粉末形貌, 但随着致密化温度的升高, 晶化和晶化相长大愈发明显, 合金密度呈增高趋势。对粉末致密化的机理进行了讨论, 认为非晶相的粘滞流动是低温下获得高致密度的主要原因。     

温度场对热力模拟压缩试验变形行为影响的数值模拟研究

针对热力模拟压缩变形试验中由于模具与材料之间的隔热效果不理想导致的试样端部温度下降造成的试样温度场不均匀情况,对热力模拟压缩试验的影响使用数值模拟方法进行了研究,考察了不同温度场分布对于压缩试验中的变形抗力、变形后试样应变分布和应变速率的影响.结果表明,温度场的分布对载荷力、应变和应变速率的分布都有较大影响,会影响热力模拟压缩试验结果的正确性.     

Effect of fiber strength on the room temperature

To increase understanding of what controls SCS-6 SiC/Ti-24Al-11Nb (at. pct) composite strength, fibers of known strength were incorporated into composites and the effect of fiber strength variability on room temperature composite strength was investigated. Fiber was also etched out of a composite fabricated by the powder cloth technique, and the effect of the fabrication process on fiber strength was assessed. The strength of the composite was directly correlated with the strength of the as-received fiber. Fabrication by the powder cloth technique resulted in only a slight degradation of fiber strength. Examination of failed tensile specimens revealed periodic fiber cracks, and the failure mode was concluded to be cumulative.     

球团矿抗压强度对其冶金性能的影响

对一种细粒度磁铁精矿粉制备的生球团,通过调整其预热及焙烧工艺参数,生产出不同抗压强度的球团矿,并对其孔隙率以及还原度和还原膨胀率进行了测定。试验结果表明,随着球团矿抗压强度的提高,其孔隙率呈下降趋势,其900℃还原度也呈下降趋势,而还原膨胀率变化不大。对不同抗压强度球团矿的矿相进行了测定,结果表明,预热时间的延长,使球团初期的预热氧化过程更加完全,Fe2O3微晶键更好地发育和长大,而焙烧温度的升高,则可以促进后期Fe2O3的再结晶和长大,提高晶键互连程度,晶粒紧密连接成片,孔隙率下降,使焙烧球团具有较高的抗压强度,但结构致密,变得难以还原。     

H13钢高温压缩过程中温升对其变形行为及组织的影响

根据热锻工艺温度-时间特征,利用Gleeble-3800热模拟试验机对H13钢进行高温压缩试验,在变形温度为800~1 100℃,变形速率为0.1~10s-1条件下获得真应力-真应变曲线。试验结果表明:压缩过程中,外力做功会导致样品温度升高,温升幅度随变形速率的增加而增大,在较低温度下变形时温升更为显著,这部分温升有利于促进动态再结晶的软化过程。由此导致900℃以下变形的试样在更小应变下就可发生再结晶,其峰值应力不会随变形速率升高而增大,甚至略微降低,呈现出较好塑性。相同变形温度下,变形后的晶粒尺寸随温升幅度的增加而增大。     

The effect of temperature and extrusion speed on the consolidation of zirconium-based metallic glass powder using equal-channel angular extrusion

In this study, gas-atomized amorphous Zr_58.5Nb_2.8Cu_15.6Ni_12.8Al_10.3 (Vitreloy 106a) containing 1280 ppmw oxygen was consolidated by equal-channel angular extrusion (ECAE). The powder was vacuum encapsulated in copper cans and subjected to one extrusion pass in the temperature region above the glass transition temperature (T _g) and below the crystallization temperature (T _x). The effects of extrusion temperature and the extrusion rate on microstructure, thermal stability, hardness, and compressive strength are investigated. Compression fracture surfaces were examined to determine the deformation mechanisms. The consolidates in which the time-temperature-transformation (TTT) boundary was not crossed during processing exhibit differential scanning calorimetry (DSC) patterns similar to the initial powder, with a slight decrease in T _x. Compressive strengths of about 1.6 GPa are recorded in the consolidates processed at 30 °C and 40 °C below T _x, which is close to what is observed in cast counterparts. The fracture surfaces exhibit vein patterns covering up to 90 pct of the surface area in some samples, which are characteristic of glassy material fracture. The slight decrease in T _x after consolidation is attributed to thermal-history-dependent short-range order and formation of nanocrystalline islands. The present results show that ECAE is successful in consolidation of metallic glass powder. This processing avenue opens a new opportunity to fabricate bulk metallic glasses (BMGs) with dimensions that may be impossible to achieve by casting methods.     

Effect of low-temperature shock compression on the microstructure and strength of copper

Copper with two purities (99.8 and 99.995 pct) was subjected to shock compression from an initial temperature of 90 K. Shock compression was carried out by explosively accelerating flyer plates at velocities generating pressures between 27 and 77 GPa. The residual microstructure evolved from loose dislocation cells to mechanical twins and, at the 57 and 77 GPa pressures, to complete recrystallization, with a grain size larger than the initial one. The shock-compressed copper was mechanically tested in compression at a strain rate of 10⁻³ s⁻¹ and temperature of 300 K; the conditions subjected to lower pressures (27 and 30 GPa) exhibited work softening, in contrast to the conventional work-hardening response. This work softening is due to the uniformly distributed dislocations and the formation of loose cells, evolving, upon plastic deformation at low strain rates, into well-defined cells, with a size of approximately 1 μm. The 99.995 pct copper subjected to the higher shock-compression pressures (57 and 77 GPa) exhibited a stress-strain response almost identical to the unshocked condition. This indicates that the residual temperature rise was sufficient to completely recrystallize the structure and eliminate the hardening due to shock compression. Thermodynamic calculations using the Hugoniot-Rankine conservation equations predict residual temperatures of 570 and 1000 K for the 57 and 77 GPa peak pressures, respectively. This article is based on a presentation given in the symposium “Dynamic Deformation: Constitutive Modeling, Grain Size, and Other Effects: In Honor of Prof. Ronald W. Armstrong,” March 2–6, 2003, at the 2003 TMS/ASM Annual Meeting, San Diego, California, under the auspices of the TMS/ASM Joint Mechanical Behavior of Materials Committee.     

Effect of temperature on the structure of liquid iron

Review of published data on the properties of liquid iron at different temperatures. Conclusion supporting a proposal that a structural change takes place in the melt.     

Effect of growth temperature on the cryopreservation of prototheca

The temperature at which Prototheca spp. were grown determined their response to freezing to -196 degrees C and subsequent thawing. Cells cultured at 35 degrees C were the most sensitive to freezing injury; at lower growth temperatures, resistance to freezing damage was seen. At all culture temperatures examined, the freezing tolerance varied with the age of the culture.