Transient Liquid-Phase Sintering Characteristic of W-Ni-Fe Alloy via Microwave-Assisted Heating

研究了W-Ni-Fe合金在2.45 GHz微波炉中瞬时液相烧结的致密化行为和力学性能。结果表明:微波辅助热场下的93W-Ni-Fe合金显示出优异的力学性能和快速的致密化过程,其压缩试样在1500℃下烧结5 min后,拉伸强度、延伸率、相对密度和硬度(HRC)分别是1200 MPa,16.6%,98.6%和42.0;在微波辅助热场下,试样烧结可以减少80%的烧结时间;微波辅助热场下的瞬时液相烧结有利于减少烧结时间,加快致密化过程,并且有利于钨晶粒的细化,获得组织均匀和综合性能高的W-Ni-Fe合金。     

Effect of heating mode and sintering temperature on the consolidation of 90W-7Ni-3Fe alloys

The present study compares the sintering response of 90W-7Ni-3Fe alloys consolidated in a 2.45 GHz microwave furnace and a conventional furnace. The W-Ni-Fe compacts were sintered in a temperature range of 1200-1500 °C corresponding to solid-state as well as liquid phase sintering. The compacts were successfully sintered in a microwave furnace with about 80% reduction in the overall processing time. For both the heating modes, the W-Ni-Fe alloys exhibited significant densification prior to melt formation through solid-state sintering. The in situ dilatometric studies revealed that the contribution to densification from solid-state sintering is higher at lower heating rates. In comparison to conventional sintering, microwave sintered compacts showed relatively refined microstructure and higher hardness and flexural strength.     

Effect of heating mode on sintering of ferrous compacts through powder metallurgy route

Abstract

Microwave heating is recognised for its various advantages, such as time and energy saving, very rapid heating rates, considerably reduced processing cycle time and temperature, fine microstructures and improved properties. The present paper focuses on preliminary work carried out with the use of microwave radiation applied to sintering of ferrous compacts. The ferrous alloy compacts were sintered in a multimode microwave furnace of 2·45 GHz and 6 kW nominal power at 1120°C for 60 min in forming gas. Results of densification, mechanical properties and microstructural evaluation of the microwave sintered samples are reported and compared with conventionally sintered ones. In general, it is observed that the microwave radiation generally enhances the properties of the sintered material when compared with conventionally sintered material.     

Effect of Ni addition on the densification of TiC: A comparative study of conventional and microwave sintering

This study deals with the effect of conventional sintering and microwave sintering on the densification kinetics of Titanium Carbide (TiC) in the presence of Ni (1, 1.5, 2 wt%). TiC compacts were obtained after uniaxial pressing of powders synthesised by ball milling of Titanium and Carbon and sintering was done in the presence of Nickel. The samples prepared were subjected to conventional as well as microwave sintering. The XRD and SEM analysis were used for a study of the reaction of Ti and C powders upon addition of Ni, which reduced the sintering temperature to 1200 °C. The densification of TiC powders was due to the Ti-Ni eutectic system, the liquid phase formed at this temperature assisting the sintering process. The SEM images revealed the flake like structure of TiC in which the carbon diffused into Ti upon the addition of Ni, thereby supporting enhanced mass transfer. The XRD pattern showed the presence of Titanium Oxide (TiO₂) along with TiC which resulted in non-uniform distribution of hardness. Maximum hardness was achieved in the conventional sintered compacts which gradually increased with increase in Ni addition. The presence of the oxide phase and the formation of micro cracks resulted in non-uniform hardness for microwave sintered compacts. The maximum hardness of conventional sintered compact (375 HLD) was nearly 1.5 times more than the maximum hardness of the microwave sintered compact (250 HLD). The density of the microwave sintered compact was found to be higher by 8% than with the conventionally sintered compact.     

溶胶-喷雾干燥超细/纳米晶W-20Cu复合粉末的烧结行为

采用喷雾干燥-氢气还原法制备超细/纳米晶W-20Cu(质量分数,%)复合粉末,粉末压坯直接从室温推入高温区烧结不同时间后直接取出水淬,研究其烧结致密化和显微组织的变化。结果表明,超细/纳米晶W-20Cu粉末在1000～1200℃烧结时发生迅速致密化。粉末压坯在1200℃烧结60min,其材料致密度已达到96.4%。1420℃烧结90min时致密度达到99%以上。1100～1420℃烧结时其烧结致密化活化能不断减小,从1100℃时的276.3kJ/mol减小到1420℃时的29.1kJ/mol。当温度低于1200℃时,W晶粒长大不明显,当温度超过1300℃时,W晶粒开始有明显长大。随温度的升高W晶粒发生显著球形化,1420℃烧结时发现其晶粒长大符合G3=kt的Ostwald机制,此时晶粒长大动力学系数K仅为0.024μm3/min。     

VC, Cr3C2 and NbC doped WC–Co cemented carbides prepared by pulsed electric current sintering

WC–12 wt.% Co grade cemented carbides doped with 0.9 wt.% VC, NbC or Cr₃C₂ grain growth inhibitor were consolidated by pulsed electric current sintering (PECS), also known as spark plasma sintering (SPS), in the solid state at 1240 °C for 2 min. The microstructure and properties of the PECS material grades are compared with those of pressureless sintered grades, liquid phase sintered at 1420 °C for 1 h. Microstructural and hardness characterization revealed that both the chemical composition and sintering technique play an important role on the WC grain growth and final mechanical properties. To obtain a nanometer sized WC–Co microstructure, it is essential to carefully select the grain growth inhibitor in addition to the application of a fast thermal densification cycle by means of spark plasma sintering.     

合金元素P,Cu含量对铸铁短纤维结合剂组织和性能的影响

本文研究了合金元素磷和铜对铸铁短纤维烧结体显微组织和性能的影响。结果表明，合金元素磷可显著提高铸铁短纤维烧结体的密度、致密化系数和压强度。磷与铜的共同加入可进一步提高烧结体的压溃强度和硬度，同时，铜的加入可抑制由磷引起的烧结体的急剧。烧结机理随磷、铜含量的增加逐渐由固相烧结＋瞬态液烧结转变为液相烧结。     

Microstructure and properties of liquid-phase sintered tungsten heavy alloys by using ultra-fine tungsten powders

The microstructure and properties of liquid-phase sintered 93W-4.9Ni-2.1Fe tungsten heavy alloys using ultra-fine tungsten powders (medium particle size of 700 nm) and original tungsten powders (medium particle size of 3um) were investigated respectively. Commercial tungsten powders (original tungsten powders) were mechanically milled in a high-energy attritor mill for 35 h. Ultra-fine tungsten powders and commercial Ni, Fe powders were consolidated into green compacts by using CIP method and liquid-phase sintering at 1465℃ for 30 rain in the dissociated ammonia atmosphere. Liquid-phase sintered tungsten heavy alloys using ultra-fine tungsten powders exhibit full densification (above 99% in relative density) and higher strength and elongation compared with conventional liquidphase sintered alloys using original tungsten powders due to lower sintering temperature at 1465℃ and short sintering time. The mechanical properties of sintered tungsten heavy alloy are found to be mainly dependent on the particles size of raw tungsten powders and liquid-phase sintering temperature.     

微波烧结WC-Co硬质合金致密化与晶粒生长

分别采用微波烧结和常规烧结制备WC-8Co硬质合金,通过1 000~1 400℃温度范围烧结以及1 400℃保温0~240 min的微波和常规烧结实验,测量各样品的收缩率、密度和晶粒尺寸,分析其致密化行为和晶粒生长,研究烧结温度和保温时间对合金致密化和晶粒生长的影响。结果表明,与常规烧结比较,微波烧结促进YG8硬质合金的致密化,且获得的合金组织均匀,晶粒细小。另外,保温时间对微波烧结YG8硬质合金的晶粒生长几乎没有影响。     

烧结温度和保温时间对微波制备WC-8Co硬质合金显微组织的影响(英文)

采用2.45GHz高功率多模腔微波炉制备WC8Co硬质合金,对压坯的收缩率和合金的显微组织进行研究。结果表明:液相温度出现在1300°C附近;在烧结温度1450°C下保温5min能获得几乎全致密的合金试样。微波烧结法制备的合金晶粒要比真空烧结制备的合金晶粒尺寸细小且分布更均匀。另外,WC晶粒的尺寸和分布主要取决于烧结温度;保温时间对合金晶粒的影响很小,无论在1450°C下保温多长时间WC平均晶粒的尺寸始终保持在2.7μm。     

Sintering process and grain growth of Mn-Zn ferrite nanoparticles

The density, microstructure and magnetic properties of non-doped Mn-Zn ferrite nanoparticles sintered compacts were investigated. The compacts of non-doped Mn-Zn ferrite nanoparticles were sintered by segmented-sintering process at lower sintering temperature. The density of sintered samples was measured by Archimedes method, and the phase composition and microstructure were examined by XRD and SEM. The sintered Mn-Zn ferrite magnetic measurements were carried out with Vibrating Sample. The results show that the density of sintered compacts increases with the rising of sintering temperature, achieving 4.8245 g·cm-3 when sintered at 900 ℃, which is the optimal density of Mn-Zn functional ferrite needed and from the fractured surface of sintered samples, it can be seen that the grain grows well with small grain size and homogeneous distribution.     

Effect of tin addition on the microstructure development and corrosion resistance of sintered 304L stainless steels

The effect of tin powder addition on the microstructure development during sintering and corrosion resistance of the 304L-Sn metallurgical system was investigated. Specimens containing 1 to 4 wt% Sn were sintered in hydrogen at temperatures ranging from 800 to 1300 °C. During sintering at temperatures below 1000 °C, most of the liquid phase was retained at the site originally occupied by the tin powder. At temperatures above 1050°C, the tin-base liquid phase spread and uniformly distributed among the 304L solid particles. Adding tin powder and the resultant liquid phase led 304L powder compacts to expand during sintering. An immersion test in 1 M H₂SO₄ and metallographic observation showed that pitting always initiated at the spots with lower tin content, and the tin atom enrichment had the beneficial effect of improving the corrosion resistance of sintered 304L stainless steels.     

Enhanced sintering, microstructure evolution and mechanical properties of 316L stainless steel with MoSi2 addition

Sintering 316L stainless steel to near full density with an appropriate sintering additive can ensure high mechanical properties and corrosion resistance. We present here a sintering approach which exploits the dissociation of ceramics in steels at high temperatures to activate sintering densification to achieve near full dense 316L stainless steel materials. MoSi₂ ceramic powder was used as a sintering additive for pre-alloyed 316L stainless steel powder. Sintering behavior and microstructure evolution were investigated at various sintering temperatures and content of MoSi₂ as sintering additive. The results showed that the sintering densification was enhanced with temperature and MoSi₂ content. The distribution of MoSi₂ was characterized by XMAPs. It was found that MoSi₂ dissociated during sintering and Mo and Si segregated at the grain boundaries. Excess Mo and Si were appeared as separate phases in the microstructure. Above 98% of theoretical density was achieved when the specimens were sintered at 1300 °C for 60 min with 5 wt.% MoSi₂ content. The stainless steel sintered with 5 wt.% MoSi₂ exhibited very attractive mechanical properties.     

Self-compacting high density tungsten–bronze composites

Green compacts of W–bronze were encapsulated in shells of bronze powder, placed in a ceramic mold and sintered in alumina tube furnace at 1150 °C. Throughout the sintering cooling stage the differential coefficient of thermal expansion ΔCTE of W–bronze was employed to induce an external compressive densification action. The process included simultaneous sintering, hot isostatic pressing (HIP) and infiltration act to enhance densification. By this technique, pilot sintered compacts of different W50–80 wt.%–pre-mix bronze of 97–99% theoretical density were produced. This process resulted in compacts of higher hardness, higher sintered density and better structure homogeneity as opposed to similar compacts densified by the conventional sintering process. The results showed a gain in hardness by 10–20% and in density by 5–15%. The impact of different cooling rates of 3, 4, 8 and 30 °C min^?1 on sintered density, microstructure and densification mechanisms was examined and evaluated. Low cooling rates of 3 and 4 °C min^?1 gave the best results.     

Mo_2FeB_2基金属陶瓷烧结过程中显微组织和力学性能的变化

采用真空烧结法制备了Mo2FeB2基金属陶瓷。运用XRD、SEM、EDS研究了Mo2FeB2基金属陶瓷的烧结过程中显微组织的变化并测试了不同烧结温度下所得金属陶瓷材料的力学性能。实验结果表明:进入L1液相(奥氏体+Fe2B)烧结阶段后,金属陶瓷由于颗粒重排致密度大幅度提高,但溶解-析出过程进行得较缓慢,晶粒基本没有长大。提高烧结温度至L2液相(奥氏体+L1+Mo2FeB2)生成后,由于溶解-析出过程明显加剧,晶粒长大趋势明显,但致密化程度进一步提高。当烧结温度达到1280℃,保温时间为40min时,烧结体接近完全致密,所得材料组织均匀具有较佳力学性能。     

Processing and mechanical properties of porous 316L stainless steel for biomedical applications

Highly porous 316L stainless steel parts were produced by using a powder metallurgy process, which includes the selective laser sintering（SLS） and traditional sintering. Porous 316L stainless steel suitable for medical applications was successfully fabricated in the porosity range of 40%-50% （volume fraction） by controlling the SLS parameters and sintering behaviour. The porosity of the sintered compacts was investigated as a function of the SLS parameters and the furnace cycle. Compressive stress and elastic modulus of the 316L stainless steel material were determined. The compressive strength was found to be ranging from 21 to 32 MPa and corresponding elastic modulus ranging from 26 to 43 GPa. The present parts are promising for biomedical applications since the optimal porosity of implant materials for ingrowths of new-bone tissues is in the range of 20%-59% （volume fraction） and mechanical properties are matching with human bone.     

Spark plasma sintering and in vitro study of ultra-fine HA and ZrO2–HA powders

Spark plasma sintering (SPS) was employed to sinter RF suspension plasma sprayed HA ultra-fine powders and ZrO₂–HA nano-composite powders. The powders were sintered at 1000 °C for 5 min at 11.1 MPa and 1100 °C for 5 min at 11.1 MPa, respectively. After sintering, the samples were ground and polished for subsequent indentation and microscopy studies. The as-sintered compacts of the HA–CaP powders were studied in vitro by immersion in simulated body fluid (SBF). The in vitro studies indicated that a bio-active apatitic layer was formed as early as 1 week after immersion. Optical microscopy and SEM investigation revealed negligible porosity and dense microstructure suggesting liquid phase sintering to have taken place. Phase composition was calculated with the aid of XRD and the Rietveld method. The results indicated that the mechanical properties of the as-sintered compacts were improved in the presence of nano-ZrO₂. The Young’s modulus increased to 130 MPa and the fracture toughness was 1.6 MPa m^1/2 for ZrO₂ loading lower than 3 vol.% indicating greater enhancement of properties than that suggested by the rule of mixtures.     

TiO2电化学还原法提取金属钛的阴极制备工艺

研究TiO2电化学还原法提取金属钛的阴极制备参数——烧结温度和烧结时间。采用SEM、EDS等方法研究烧结温度、烧结时间对TiO2阴极微观结构、孔隙率的影响及不同烧结条件下TiO2阴极电解产物结构和氧含量的变化。结果表明：烧结条件主要影响电极的粒度大小、孔隙尺寸和孔隙分布：在较高温度下烧结较长时间获得的电极片粒度较粗,而孔隙率的变化比较复杂。电极的颗粒尺寸、孔隙率直接影响脱氧率：粒度较小的电极在试验条件下可被充分还原;电极中的开孔和闭孔都有利于电化学还原过程的进行。在1000~1100 °C下烧结4 h获得的TiO2阴极脱氧效果较好。     

Influence of spark plasma sintering on microstructure and wear behaviour of Ti-6Al-4V reinforced with nanosized TiN

Ti-6Al-4V/TiN composites were successfully consolidated by spark plasma sintering (SPS). TiN addition to Ti-6Al-4V was varied from 1% to 5% (volume fraction). The effect of TiN addition on the densification, microstructure, microhardness and wear behaviour of Ti-6Al-4V was studied. Experimental results showed reduction in sintered density of the compacts from 99% to 97% with increase in TiN content. However, an increase in microhardness value was recorded from HV_0.1 389 to HV_0.1 488. X-ray diffraction (XRD) analysis showed that the intensity of diffraction peaks of TiN phase in the composites increased also with formation of small amount of secondary Ti₂N phase. SEM analysis of SPS sintered nanocomposites possessed a refinement of α/β phase microstructure in Ti-6Al-4V with the presence of uniformly dispersed TiN particles. The worn surface of the composite showed improved abrasive wear resistance with non-continuous grooves as compared to the sintered Ti-6Al-4V without TiN addition.     

Effects of rare earth addition on sintering process and dielectric property of cordierite based glass-ceramics

The effects of rare earth oxide on the sintering and dielectric property of cordierite-based glass-ceramics with non-stoichiometric composition prepared by quenching of molten droplets were investigated. The results show that the addition of rare earth oxide can lower the sintering temperature of cordierite glass-ceramics, improve the densification process and obviously reduce sintering activation energy. It is found that the densification of cordieritebased glass-ceramics is a liquid phase sintering process. The dielectric constant of the sintered compacts enhances with the increase of the density. When the sintering temperature is identical, the rare earth addition is found to have a noticeable effect on the dielectric loss of glass-ceramics. The properties of the glass-ceramics containing rare earth oxide appear to be correct for low firing temperature substrates.