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.     

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.     

微波烧结对粉末冶金铁基材料性能的影响

采用微波烧结新技术研究了粉末冶金铁基材料的烧结工艺与性能，并同常规真空烧结工艺进行了比较。结果表明：微波烧结粉末冶金铁基材料在1280℃的烧结温度下保温10min时，可达到95．8％的相对密度；烧结温度降低。烧结时间大幅度缩短，且微波烧结制品的孔隙明显减小或消失，硬度、抗弯强度、抗拉强度均有较大幅度提高。     

微波烧结温度对CNTs/Cu复合材料结构和性能的影响

结合液相混合方法、微波烧结技术和冷轧技术制备碳纳米管增强铜基（carbon nanotubes reinforced copper-matrix,CNTs/Cu）复合材料,研究不同烧结温度对于CNTs/Cu复合材料微观形貌、力学性能及物理性能的影响。结果表明,采用液相混合法制备出粒径为200~500 nm、碳纳米管质量分数为0.5%的CNTs/Cu复合粉体,碳纳米管均匀分散在铜颗粒中,并与之形成良好结合界面。CNTs/Cu复合材料的相对密度、硬度、电导率随着烧结温度的升高先增大后减小,在烧结温度为1000℃时达到最佳。制备的碳纳米管质量分数为0.5%的CNTs/Cu复合材料组织均匀、孔隙数量及尺寸较少,相对密度为95.79%,硬度为HV 80.9,电导率为81.8% IACS。经冷轧处理后,CNTs/Cu复合材料拉伸强度达到218 MPa,延伸率保持37.75%。由此可见,微波烧结技术是一种制备高性能CNTs/Cu复合材料的理想方法。     

SPS烧结制备WC-6Co-1.5Al硬质合金的研究

针对WC-6Co-1.5Al球磨粉末,研究SPS烧结工艺对烧结合金密度、组织、力学性能及断口形貌的影响规律.研究结果表明：在脉冲电流基值为360A、峰值为3 000A、频率为50Hz、占空比为50%,恒流电流为1 500A,总烧结时长为6min,烧结压力为30MPa的工艺参数下,利用脉冲电流烧结1min后,继之以恒流电流烧结5min,可获得密度、硬度和弯曲强度分别达14.2g/cm3、94HRA和1 660MPa的超细晶WC-6Co-1.5Al硬质合金块体材料;进一步延长或缩短脉冲电流烧结时间,烧结体的密度、硬度和弯曲强度反而下降.     

镀钨碳纳米管增强铜基复合材料的制备及性能

采用羰基热分解法对多壁碳纳米管表面进行镀钨处理,并以镀钨碳纳米管和电解铜粉为原料,进行机械球磨混粉和放电等离子体烧结,制备了镀钨碳纳米管/铜基复合材料.采用场发射扫描电镜观察了粉体和复合材料的组织形貌,并对复合材料物相进行了X射线衍射分析.探讨了镀钨碳纳米管含量和放电等离子体烧结温度对复合材料致密度、抗拉强度、延伸率和电导率的影响.结果表明,镀钨碳纳米管质量分数为1%和烧结温度为850℃时,复合材料的致密度、抗拉强度和电导率最高.与烧结纯铜相比,复合材料的抗拉强度提高了103.6%,电导率仅降低15.9%.     

Effect of conventional and microwave sintering on the properties of yttria alumina garnet-dispersed austenitic stainless steel

The current study examines the effect of heating mode, temperature, and varying yttria alumina garnet (YAG) addition (5 and 10 wt pct) on the densification and properties of austenitic (316L) stainless steel. The straight 316L stainless steel and 316L-YAG composites were heated in a radiatively heated (conventional) and 2.45 GHz microwave sintering furnace. The compacts were consolidated through solid state as well as supersolidus sintering at 1200 °C and 1400 °C, respectively. Both 316L and 316L-YAG compacts couple with microwaves and heat to the sintering temperature rapidly (∼45 °C/min). The overall processing time was reduced by about 90 pct through microwave sintering. As compared to conventional sintering, compacts sintered in microwaves exhibit higher densification and finer microstructure but no corresponding improvement in mechanical properties and wear resistance. This has been correlated to elongated, irregular pore structure in microwave-sintered compacts.     

Effect of Cu3P addition on sintering behaviour of elemental powders in the composition of 465 stainless steel

Abstract

The addition of Cu₃P for developing the high strength 465 maraging stainless steel from elemental powders was studied. The sintering parameters investigated were sintering temperature, sintering time and wt-%Cu₃P. In vacuum sintering, effective sintering took place between 1300 and 1350°C. The maximum sintered density of 7·44 g cm^?3 was achieved at 1350°C for 60 min with 4–6 wt-%Cu₃P. More than 6 wt-%Cu₃P content and temperature >1350°C caused slumping of the specimens. The sintered specimens were heat treated and a maximum ultimate tensile strength (UTS) of 767 MPa was achieved with 4 wt-%Cu₃P content. The maximum hardness of 45·5 HRC was achieved in heat treated condition with 4 wt-%Cu₃P content. Above 4 wt-%Cu₃P content increase in density was observed whereas the response to heat treatment decreased. Fracture morphologies of the sintered specimens were also reported. A comparison of sintering behaviour and mechanical properties of elemental powders with prealloyed powders was also given in the present study.     

W-Ni-Cu-Sn系高比重合金的研究

本文研究了烧结温度、保温时间以及添加锡对W-Ni-Cu合金性能的影响。结果表明,不添加锡的93W-Ni-Cu合金与添加1%Sn的85W-Ni-Cu-Sn合金相比,其烧结温度由1320℃降至1140℃,即烧结温度降低约200℃;抗拉强度从686N/mm2提高到980N/mm2;热膨胀系数提高了28%。获得了较好的综合性能。     

Microstructure,mechanical properties and tribological behaviour of PM Fe-Cu-Zn alloys containing solid lubricants

Abstract

Fe-Cu-Zn alloys containing solid lubricants of graphite and talc produced via cold pressing and sintering technology are investigated. The influence of composition and sintering temperature on open porosity, density, strength and hardness of these alloys is studied. The microstructure is correlated with the mechanical properties of the sintered materials. The tensile tests showed that the peak strength was observed for samples sintered at ≤1000°C. Above this temperature the bending and tensile strength values decrease. Microstructural analysis of sintered materials revealed three phases in the structure: α-Fe, α-brass and talc. Results indicate that the microstructure of sintered samples is sensitive to process variables such as brass and talc contents and sintering temperature.     

Effect of molybdenum additives on the mechanical properties of iron-copper pseudoalloys

The effect of molybdenum additives (10%) on mechanical properties and the microstructure of iron-copper (Fe-30% Cu) pseudoalloys is investigated. The tensile strength, hardness, and electrical resistivity are determined, and the microstructure of specimens is analyzed quantitatively. It is established that during both solid-and liquid-phase sintering, no solid-phase solutions are formed, and a stable heterophase microstructure develops as the components undergo mutual diffusion. The heterophase nature of structure hinders grain growth of the refractory phase. The grain size of the sintered specimens does not exceed 1–5 µm. The plasticity of Fe-30% Cu-10% Mo pseudoalloys obtained during solid-phase sintering is increased significantly as compared with Fe-Cu alloys, and the elongation is 13.8% at a porosity of about 1%. Specimens produced by liquid-phase sintering experience greater elongation, but during prolonged liquid-phase sintering (more than 10 min), grain growth is restored, and the plasticity of the Fe-Cu-Mo specimens is reduced.     

烧结温度对Fe-Cu-Mo-C合金组织和性能的影响

采用机械球磨混粉和真空烧结相结合的方法制备了Fe-Cu-Mo-C合金,研究了不同烧结温度对粉末冶金Fe-Cu-Mo-C合金材料的显微组织、密度、抗拉强度和摩擦磨损性能的影响。结果表明:随着烧结温度由1 000℃升高到1 100℃,Fe-Cu-Mo-C合金烧结体组织孔隙数量减少、孔隙尺寸明显降低;当烧结温度提高到1 150℃时,烧结体组织中孔隙尺寸增大。随着烧结温度升高,烧结体的密度、硬度、抗拉强度和伸长率先增大后减小,磨损量先降低后升高。最佳烧结温度为1 100℃,此时烧结体的密度为6.90 g/cm3,抗拉强度为319 MPa,洛氏硬度为34.7 HRC,磨损量为0.087 g。     

铜包覆石墨烯增强316L奥氏体不锈钢力学性能研究

采用分子水平混合和低速球磨的方法制备铜包裹石墨烯/316 L不锈钢复合粉体,通过放电等离子烧结制备石墨烯增强316 L奥氏体不锈钢复合材料,研究铜及石墨烯对复合材料密度、硬度和拉伸性能的影响,并对拉伸断口形貌进行了分析.结果表明:通过分子混合和球磨混合可制备铜包裹石墨烯与不锈钢均匀混合的复合粉体.烧结过程石墨烯结构保持完整.铜包裹石墨烯增强体可明显改善烧结不锈钢复合材料的密度、硬度、抗拉强度和屈服强度,使其分别提高3.6%、17.4%、35.8%和34.5%.     

Effect of Sinter Hardening on Microstructure and Mechanical Properties of Astaloy 85Mo

 Effect of sinter hardening on the microstructure, density, hardness and tensile properties of Astaloy 85Mo+0.7% graphite was investigated. For this purpose, Astaloy 85Mo, a pre-alloyed powder, was mixed with 0.7% UF4 graphite and then pressed in single action die and sintered at 1120 ℃ for 30 min in N2-10%H2 atmosphere. Then samples were cooled from 0.5 to 3 ℃/s sintering temperature in accordance with different cooling rates. The difference in microstructure, hardness, density and tensile properties of the samples associated with different cooling rates from sintering temperature has been investigated. The results show that the microstructure remains bainitic by changing cooling rate, but it becomes finer and then the hardness and tensile strength of the samples will increase by increasing the cooling rate from sintering temperature.     

微波烧结与传统烧结对纯钛组织与性能的影响

和熔炼铸造法相比,采用粉末冶金法制备钛材,可以避免引入杂质,提高原料利用率。本文探讨微波烧结与传统烧结对纯钛组织及性能的影响,结果表明,在1200℃保温2 h传统烧结得到等轴α-Ti组织,密度为4.33 g·cm-3,相对密度为96.06%,硬度为HV 260,抗压强度为1309 MPa,断面膨胀率为10.63%,呈典型的解理状脆性断裂;在1200℃保温15 min微波烧结得到等轴的α-Ti与条状β-Ti组织,密度为4.30 g·cm-3,相对密度为95.45%,硬度为HV 311,抗压强度为1175 MPa,断面膨胀率为18.89%,展现出一定的塑性,呈准解理状脆性断裂。     

Consolidation of aerospace grade aluminum 7055 powder through SPS-forge processing

The objective of this research was to assess the SPS-forge response of fully pre-alloyed aerospace grade 7055 (Al–8Zn–2.1Mg–2.3Cu–0.2Zr) powder. The core variables investigated were the sintering temperature, time, and atmosphere employed, as well as the average particle size and the manner of uni-axial loading. Samples sintered in vacuum at 500°C for 40?min with delayed loading offered the most desirable combination of density, hardness, and bend properties but remained relatively brittle. Hot forging of the sintered preforms was found to impart sizable gains in mechanical properties. The SPS-forge product exhibited tensile yield strength of 603?MPa coupled with a ductility of 9.1% and a hardness of 93 HRB. All such properties were largely equivalent to those measured for the wrought counterpart.     

放电等离子烧结制备超细晶WC-3Co硬质合金的组织和性能

采用高能球磨制备纳米WC-3Co粉末,再通过放电等离子烧结(spark plasma sintering,SPS)制备超细晶WC-3Co硬质合金。研究SPS工艺参数对合金致密度、显微组织和力学性能的影响,并对SPS和热压工艺(hotpressing,HP)进行对比。结果表明:SPS可实现WC-3Co粉末的低温快速致密化。升高温度或提高压力都使得合金的致密度提高,同时导致WC晶粒长大。SPS较HP升温速率快且烧结时间更短,合金组织更加均匀,在1 300℃保温5 min、烧结压力为40 MPa的条件下所制备的合金具有最佳综合性能,其平均晶粒度为0.32μm,相对密度、硬度、抗弯强度、断裂韧性分别为99.3%、2257 HV30、1 906 MPa、10.36 MPa.m1/2。而在1 450℃、压力为50 MPa、保压5 min条件下,热压合金的致密度、硬度和断裂韧性分别为99.6%、2 264 HV30和11.01 MPa.m1/2,但抗弯强度只有1 301 MPa,平均晶粒度为0.47μm。     

The properties of tungsten processed by chemically activated sintering

Two tungsten powders have been treated with small concentrations of sintering activators to provide for enhanced low temperature sintering. The experimental study focused on the determination of the processing effects on properties such as sintered density, grain size, hardness, and strength. Variables in the plan included tungsten particle size, type of activator, amount of activator, compaction pressure, and sintering temperature. The sintered density is found to have a dominant effect on strength and hardness. The various processing variables are analyzed in terms of their effects on density. At high sintered densities, grain growth acts to degrade the strength. Additionally, the nature of the sintering activator influences the fracture strength. In this study optimal strength occurred with a 0.7 μm tungsten powder treated with 0.29 wt pct Ni, sintered at 1200 °C for one hour. The resulting density was 18.21 g/cm³, with aR _A hardness of 69 and a transverse rupture strength of 460 MPa.     

Combined effects of time and temperature on strength evolution using integral work-of-sintering concepts

Sintered materials have significantly higher strength than green compacts. The evolution of that strength during the sintering cycle involves a combination of annealing, thermal softening, and sintering events. The dynamic interplay between heating rate, sintering time, and sintering temperature controls the in situ strength and determines the final sintered strength. Although sintered strength is a well-explored subject, the dynamic evolution of strength requires new models. This research has measured both the sintered and in situ strengths as functions of heating rate, hold times, and temperature for die-compacted prealloyed bronze powder. A core concept is the use of an integral work of sintering to determine the effective strengthening due to sintering. The model is used to map strength evolution vs the key processing parameters. It is concluded that, during solid-state sintering of bronze, the key sources of distortion are the density and thermal gradients.     

纳米AlN颗粒弥散增强铜基复合材料的制备及性能研究

本文采用高能球磨结合放电等离子烧结法制备了含不同质量分数AlN的AlN/Cu复合材料。研究了AlN质量分数对AlN/Cu复合材料微观形貌、相对密度、显微维氏硬度、拉伸强度、延伸率及导电性能的影响。结果表明:当AlN质量分数1.0%时,随着AlN质量分数的提高,复合材料的硬度、抗拉强度提高,断后伸长率、电导率降低。但当AlN质量分数为1.0%时,AlN/Cu复合材料相对密度为97.8%,显微硬度和抗拉强度分别达到了HV 119.5和259.7 MPa,电导率为49.30 mS·m~(-1),综合性能达到最优。