真空度及碳含量对M2高速钢组织和拉伸性能的影响

采用真空烧结工艺制备M_2高速钢,研究真空度与碳含量对高速钢组织和拉伸性能的影响。结果表明:低真空度下(10-1 Pa)M_2高速钢的有效烧结温度为1 220～1 230℃,在该区间内烧结相对密度可达96%以上,烧结体显微组织由奥氏体基体及M_6C、MC碳化物组成;超过该温度区间进行烧结会使合金析出有害的共晶碳化物,导致高速钢强度显著下降。当真空度提高到10~(-3) Pa时,M_2高速钢的烧结温度降低,显微组织中的碳化物更细小、分布更均匀。M_2高速钢的相对密度为98%,拉伸强度为989 MPa,伸长率为7.1%。随碳含量升高,M_2高速钢的烧结区间无明显变化,但在较低温度下烧结更容易实现致密化。当碳的质量分数为1.0%时,样品的相对密度为97%,拉伸强度为954 MPa,伸长率为7%。     

烧结温度对氧化铪粉末性能的影响及喷涂涂层性能研究

本试验采用喷雾干燥 - 高温烧结的方法制备了氧化铪粉末, 并采用大气等离子喷涂 (APS) 技术在钢基体表 面制备了氧化铪涂层, 研究了烧结温度对氧化铪粉末以及涂层微观组织和性能的影响。 结果表明随着烧结温度从 1000 ℃升高至 1300 ℃, 氧化铪粉末微观组织变化不明显, 微颗粒也未发生明显长大, 当温度升高至 1400℃以上 时, 粉末内部组织逐渐变得致密, 微颗粒开始微熔连接, 形成网络状骨架; 当烧结温度为 1000 ℃至 1300 ℃时, 粉末颗粒强度处于相对较低的水平, 随着烧结温度升高至 1400 ℃、 1500 ℃时, 粉末颗粒强度逐渐增大; 1400 ℃ 烧结后的氧化铪粉末经大气等离子喷涂形成的涂层组织均匀结构较致密, 涂层孔隙率为 3.9%, 涂层平均显微硬 度为 552.24 HV0.3, 涂层结合强度均值达到 24.78 MPa。     

热等静压铁钴镍基高温合金的显微组织和力学性能

以气雾化（gas atomization,GA）粉末为原料,采用热等静压（hot isostatic pressing,HIP）致密化烧结工艺制备Fe18Ni23Co25Cr21Mo8WNbC2铁钴镍基高温合金,研究热等静压温度对致密化Fe18Ni23Co25Cr21Mo8WNbC2粉末高温合金金相组织、力学性能和断口形貌的影响。结果表明:热等静压技术制备的高温合金致密化程度很高,烧结体由（Fe,Ni）固溶体相和弥散分布的M6C碳化物强化相组成;热等静压温度为950~1050 ℃时,烧结体的密度、力学性能随着热等静压烧结温度的提高而提高;当热等静压温度达到1100 ℃时,致密化烧结体晶粒组织明显长大,其力学拉伸性能降低;致密化烧结体的室温拉伸断口以穿晶断裂为主,局部区域晶粒被拉伸开裂,650 ℃高温断口为穿晶断裂和沿晶断裂的混合形貌,基体相存在沿应力方向被拉长的韧窝。     

热轧不锈钢复合板界面氧化物夹杂的形成机制

 以不锈钢-低合金钢复合板为研究对象,利用光学显微镜及扫描电镜对复合界面附近的夹杂物进行了分析。研究发现,不锈钢复合板界面处夹杂物主要为氧化物,其成分与复合界面处的真空度有关。在较低的真空度下(真空度大于15Pa),氧化物夹杂的成分以硅为主,在较高的真空度下(真空度小于0.1Pa),夹杂的成分以铝为主。界面氧化物夹杂主要是由于高温下钢中的Al、Si和Mn等元素向复合界面处扩散并被氧化形成的。由试验结果也可知,随着真空度的降低,界面氧化也变得更加明显,当真空度的值从0.1Pa增加到20Pa左右时,界面氧化物的体积分数从15%提高到了50%。     

烧结压力对WC-12%Co粗晶硬质合金组织及性能的影响

研究了不同烧结压力对WC-12%Co粗晶硬质合金金相组织结构及物理力学性能的影响。结果表明:合金能够在较低的烧结压力下达到高度致密化,随着烧结压力增加,合金的三项性能没有明显的变化;当烧结压力为2 MPa左右时,合金的抗弯强度和冲击韧性最高,且具有良好的综合性能。     

W-Ni-Fe高比重合金液相烧结时的致密化

研究了W-Ni-Fe高比重合金烧结时的致密化,实验证明W-Ni-Fe合金烧结时的致密化过程具有液相烧结的特征,符合Kingery提出的方程。目前生产的W-Ni-Fe合金中粘结相常采用Ni:Fe=7:3或Ni:Fe=1:1。针对这两种成分的合金我们研究了不同温度下的收缩率、密度变化与时间的关系,并讨论了其致密化机理。     

RH真空冶炼过程中锰损

为了减少RH真空冶炼过程中钢水锰元素偏差和提高最终产品性能的稳定性,采用直读光谱仪对不同条件下RH真空冶炼镇静钢与非镇静钢锰损情况开展研究。结果表明,RH真空冶炼过程中锰损存在4种形式,与钢水中自由氧反应烧损、钢渣界面反应、合金粉末抽吸、真空锰挥发;随着钢水中锰含量增加、真空时间延长,钢水温度和氧化性提高,RH真空锰损逐渐增加;真空度小于1 000 Pa时,RH真空锰损随真空度的降低而降低,而当真空度大于1 000 Pa时,继续降低真空度,RH真空锰损几乎不变。通过降低RH真空度、进站锰含量和温度、减少RH真空处理时间等措施,RH结束目标锰的质量分数±0.01%命中率接近100%。     

高能球磨Ti/Al复合粉体的反应烧结致密行为

研究高能球磨Ti/Al复合粉反应烧结过程的致密行为 ,并进行反应烧结热力学和动力学分析。结果表明 ,与增加烧结压力、提高烧结温度或延长烧结时间的作用相同 ,高能球磨对Ti/Al粉末体反应烧结过程的致密化具有促进作用 ,且效果更加显著。球磨时间越长 ,烧结体越致密。球磨 3h的Ti/Al复合粉坯料经6 30℃× 2h预烧、12 5 0℃× 8h无压烧结后 ,获得的TiAl基合金试样的致密度高达 99 87%。球磨对Ti/Al粉末体反应烧结时致密化的促进作用 ,主要是由于Ti、Al反应组元及其晶粒尺寸的细化 ,晶格畸变能增加 ,从而显著提高了烧结驱动力和烧结动力学因子 ,缩短了反应扩散距离 ,抑制了kirkendall孔隙的形成。     

高速钢粉末真空高温处理时组织结构之变化

研究了水雾化M 2和M 4高速钢粉末在 7× 10 -2 Pa真空下加热后组织结构的变化。当粉末加热至固相线以下 15～ 2 0℃ ,即 12 2 0～ 12 2 5℃时 ,M6C及MC型碳化物都由 1～ 2 μm长大到 3～ 4 μm ;当粉末加热至固相线以上时 ,碳化物尤其是M6C型碳化物颗粒快速长大 ,并且有不均匀长大现象 ;当温度升至 12 5 0℃后 ,贫碳型的M4C3 转变为MC型碳化物 ,其中大部分Fe被V所取代 ;当进一步加热至 12 6 0℃以上时 ,M6C型碳化物将转变为M2 C碳化物。经真空脱氧后高速钢粉末的氧含量降低至 10 0× 10 -6以下。     

原位反应制备Mo_2FeB_2基金属陶瓷烧结过程热力学分析

对Fe-6B-48Mo-0.8C材料体系用液相烧结原位反应法制备了Mo2FeB2三元硼化物金属陶瓷,用SEM-EDS观察分析了烧结体的组织结构与成分组成,用热分析(DSC)、X射线衍射分析与热力学计算表征了体系的反应过程。结果表明,在该材料体系中,Fe2B、MoB2为反应中间相,Mo2FeB2为最稳定存在的相,呈条块状均匀分布在铁基粘结相中。通过热力学计算分析,在Mo-Fe-B三元体系中,Mo2FeB2的Gibbs自由能最低,形成能力最强,在481.8℃开始形成Fe2B,当温度达到1293.7℃时,该体系形成最稳定的Mo2FeB2相,并使材料致密化。     

Deoxidation of molybdenum during vacuum sintering

Molybdenum is usually fabricated through the powder metallurgy (P/M) process, using fine powders with a relatively high oxygen content. Oxygen, however, is one of the main elements causing embrittlement during the deformation processing of molybdenum, such as rolling, extrusion, and forging. Thus, how to deoxidize the compact as completely as possible is critical in the P/M process. This study shows that, as an alternative to hydrogen reduction, molybdenum oxides can be reduced by adding organic lubricants to the compact and by sintering the compact under high vacuum with long sintering times. After 10 hours of sintering at 1750 °C and a 0.03 torr vacuum, the oxygen content decreased from 0.927 wt pct of the green compact to 0.017 wt pct. The ductility also improved significantly compared to compacts sintered for 5 hours, which contained 0.218 wt pct oxygen. The morphology evolution, weight changes, and the X-ray analysis indicated that the oxide was first present in the form of MoO₃. It was then transformed into MoO₂ before deoxidation was completed. Two deoxidation mechanisms were identified: evaporation and decomposition of MoO₃ and MoO₂, with evaporation being dominant in the early-stage sintering and decomposition being dominant in the later stage.     

Optimization of microstructures and magnetic properties of Sm(CobalFe0.227Cu0.07Zr0.023)7.6 magnets by sintering treatment

Magnetic properties and microstructures of Sm(Co_(bal)Fe_(0.227)Cu_(0.07)Zr_(0.023_)_(7.6) sintered magnets were optimized by sintering treatment. Results show that the knee-point magnetic field, Hknee, is twofold up and the intrinsic coercivity Hcjincreases by 40%, ranging from 21.64 to 30.39 kOe at the cost of a little decrease of Brfrom 10.84 to 10.31 kGs with sintering temperature decreasing from 1488 to 1473 K. And the average domain width is narrower and more uniform for the specimen sintered at 1473 K than that of the specimen sintered at 1488 K. It is impressive that the density of lamellar phase increases from ~0.050 to ~0.058 nm~(-1) with the sintering temperature decreasing from 1488 to 1473 K. Moreover, the average cellular size is about ~84 nm for the magnets sintered at 1473 K, which is 80% of that of the magnets sintered at 1488 K(~97 nm). And the cell boundary width of the magnets sintered at 1473 K(~7 nm) is only half average width of the magnets sintered at 1488 K(~14 nm). It is found that the Cu content in the cell boundaries is much higher(~17 at%) in the magnets sintered at 1473 K compared to that of the magnets sintered at 1488 K(~10 at%). It can be concluded that smaller cells and narrower cell boundaries together with higher gradient of Cu content are key points for obtaining the optimum Hkneeand Hcj.     

Effect of Nd3+ substitution on structural and magnetic properties of Mg–Cd ferrites synthesized by microwave sintering technique

Nd~(3+) substituted spinel ferrites with formula Mg_xCd_(1-x)Nd_(0.03)Fe_(1.97)O_4(x = 0.0.2,0.4,0.6.0.8 and 1.0)were prepared by oxalate co-precipitation method using novel microwave sintering technique. AR grade sulphates were used as starting chemicals. The samples were sintered at optimized power of 70 W for10 min in a microwave oven(800 W). The structural analysis of these samples was done by using X-ray diffraction, scanning electron microscope and Fourier transform IR techniques. The XRD analysis of the synthesized ferrite confirms the formation of cubic spinel structure of ferrite. The influence of Nd3+substitution on various structural parameters of Mg-Cd ferrites was reported. IR study indicates the spectra contain two intense absorption bands around 600 and 400 cm~(-1) in addition with four extra bands. The magnetic properties of all ferrites were studied by using a vibration sample magnetometer.The crystallite and grain size dependant magnetic properties are observed. The composition Mg_(0.6)Cd_(0.4)Nd_(0.03)Fe_(1.97)O_4 has better magnetic properties that can be used in recording media. The fast synthesis of spinel ferrites is yielded due to use of the microwave sintering technique.     

Synthesis of pewter alloy from tin–copper–antimony powder mixtures by microwave and conventional sintering

Abstract

Two compositions of pewter alloy were sintered using both microwave and conventional vacuum sintering, and the effects of sintering time, temperature and weight percentage of copper and antimony on the mechanical and structural properties were examined for both sintering methods. Microwave sintered samples had finer microstructures, higher densities, higher hardness and tensile strength compared to the conventionally sintered samples and traditionally cast pewter. By increasing the copper and antimony contents, higher hardness was achieved. Better mechanical properties were found after microwave sintering after shorter sintering times compared with conventional sintering, but longer sintering times resulted in better diffusion for both sintering methods. The microwave sintered samples in general were capable of achieving similar amounts of diffusion to those conventionally sintered for the same time. But the total sintering process is much faster in microwave heating than in conventional heating due to the rapid heating effect.     

Corrosion mechanism of H_2O on Sm_2Fe_(17) and nitrogenation process of corroded Sm_2Fe_(17)

Sm_2 Fe_(17) prepared by reduction-diffusion method needs to be washed with water to remove calcium oxide. Electrochemical corrosion occurs when Sm_2 Fe_(17) powder is in contact with liquid water. Corrosion mechanism of H_2 O on Sm_2 Fe_(17) powder and nitrogenation process of corroded Sm_2 Fe_(17) were studied by analyzing the structure and morphology. It is indicated that the metallic hydroxide forms and deposits on the Sm_2 Fe_(17) powder surfaces during water corrosion. At the same time, oxygen and hydrogen enter the unit cell of Sm2 Fe_(17), causing a slight increase in Curie temperature. In the subsequent nitriding process,the hydroxide is dehydrated and hydrogen is desorbed. The resulting oxide reacts with Sm_2 Fe_(17)N_x to form a-Fe and Sm_2 O_3. Thermodynamic calculations using the HSC Chemistry 6.0 software indicate that the reaction can occur spontaneously. The effect of water corrosion on the magnetic properties of the nitride can be eliminated by hydrogen reduction prior to nitriding.     

Microstructure and mechanical properties of microwave sintered austenitic stainless steel

The objective of this work is focused on understanding the effect of microwave heating on sintering of 316L powders. The stainless steel samples were prepared from prealloyed powders of 316L. The powder samples were compacted at a pressure of 560 MPa and sintered at 1300°C in a microwave furnace of 2.4 GHz and 2KW capacity in nitrogen atmosphere. The sintering time was varied from 10 to 20 minutes in order to study the effect of sintering time on sintering behavior and mechanical properties of the sintered samples. The sintered samples were subjected to optical metallography, hardness testing, tensile testing and fractogrphy. The average density of sintered stainless steels was 92% of the theoretical density, approximately 18% increment from green density for 20 min. sintering time. Microstructural analysis showed the regularly distributed porosity with very small grains. The hardness value was in the range of 365VHN to 396VHN and tensile strength, in the range of 255MPa to 580 MPa. Fractographs for these steels revealed mixed mode of fracture.     

Effect of residual pressure on vacuum sintering of Ti–Ni alloys

Abstract

In earlier work the authors examined the sintering of Ti–Ni alloys by means of dilatometry of mixed elemental powders. Some notable differences were observed when heat treatments were carried out using a vacuum tube furnace rather than the dilatometer: higher sintered density was achieved due to a combination of lower heating rate and lower residual pressure, and swelling during liquid phase sintering was greatly reduced. This observation is consistent with the idea that gas pressure within closed pores causes swelling during liquid phase sintering and retardation of shrinkage in solid state sintering. In addition to the results of measurements of density and open and closed porosity as a function of Ni content and sintering temperature, macrographs and optical micrographs of the sintered compacts are presented, and the effects of heating rate and compaction pressure are described.     

Damping characteristics of pure aluminum: A comparison of microwave and conventional sintering

The current research focuses on how heating mode in powder metallurgy affects the damping properties of pure aluminum. The aluminum powder was compacted in a hydraulic press measuring 40 x 12 x 1.5mm3 and heated in a muffle furnace (conventional) and a microwave sintering furnace. The damping measurements were conducted on the samples using a dynamic mechanical analyzer under dual cantilever mode at various vibrating frequencies of 0.1, 1 and 10Hz from room temperature (RT) to 150°C at constant strain. Results demonstrated that the microwave sintered samples exhibit high storage modulus and high damping capacities compared to conventional sintered samples. The mechanisms that support this behavior are investigated and presented.     

放电等离子烧结不同粒径匹配的WC-Co混合粉末

采用一种包括混合粉末真空预处理和放电等离子烧结(SPS)的新型烧结技术,制备超细晶WC-10Co硬质合金块体。采用场发射扫描电镜观察硬质合金的形貌和晶粒组织,采用三点弯曲法测量试样的断裂强度,利用显微硬度仪测量维氏硬度HV30且据此估算试样的断裂韧性KIC,并与真空烧结和直接SPS试样进行对比,同时还研究初始粉末中WC粉与Co粉的粒径匹配对SPS块体的显微组织和力学性能的影响。结果表明,与真空烧结和直接SPS相比,此种方法制备的WC-10Co合金晶粒细小、组织均匀,具有优异的综合力学性能,尤其是强度明显提高,硬度为1608HV30,断裂韧性为14.0MPa.m1/2,横向断裂强度为3100MPa;WC和Co粉末的粒径匹配对SPS块体的显微组织和力学性能具有较显著的影响。     

Compaction and Sintering Behavior of Niobium Powder for Making Consumable Electrodes

Niobium consumable electrodes of 10?mm dia?×?50?mm length were prepared by cold isostaic pressing with compaction pressure of 125?C250?MPa. The compacts were sintered under vacuum at different temperatures in the range of 1000?C1800?oC. The CIPed and sintered electrodes were characterized with respect to chemical analysis, density, microstructure and bend strength. The results showed that there is a marginal improvement in density at a sintering temperature in the range of 1000?C1400?oC, while a significant improvement in density was observed at sintering temperature in the range of 1600?C1800?oC. The bend strength of sintered electrode was found to increase with increasing sintering temperature and that attains a highest value at a sintering temperature in the range of 1600?C1800?oC. Sintering at a temperature higher than 1400?oC leads to decrease in oxygen content of the electrodes. The oxygen content was decreased from 2000 to 500?ppm when electrode was sintered at 1800?oC.