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.     

Effects of sintering conditions on mechanical properties of mechanically alloyed tungsten heavy alloys

The effects of sintering conditions on the microstructural evolution and mechanical properties of mechanically alloyed tungsten heavy alloys were investigated. W, Ni and Fe powders were mechanically alloyed in a tumbler ball mill at a milling speed of 75 rpm, ball-to-powder ratio of 20∶1 and ball filling ratio of 15%. The mechanically alloyed powders were compacted and solid-state sintered at a temperature of 1300°C for 1 hour in a hydrogen atmosphere. The solid-state sintered tungsten heavy alloy was subsequently liquid-phase sintered at 1470°C with varying sintering times from 4 min to 90 min. The solid-state sintered tungsten heavy alloy showed fine tungsten particles of 3 μm in diameter and high relative density above 99%. The volume fraction of the W-Ni-Fe matrix phase was measured, as 11% and tungsten/tungsten contiguity was 0.74 in solid-state sintered tungsten heavy alloys. Mechanically alloyed and two-step sintered tungsten heavy alloys showed tungsten particles of 6–15 μm and a volume fraction of the W-Ni-Fe matrix phase of 16% and tungsten/tungsten contiguity of 0.40. The solid-state sintered tungsten heavy alloy exhibited a yield strength of about 1100 MPa due to its finer tungsten particles, while it showed low elongation and impact energy due to its large tungsten/tungsten contiguity. The yield strength of two-step sintered tungsten heavy alloys increased with the decreasing of tungsten particle size and volume fraction of the W-Ni-Fe matrix. This article is based on a presentation made in “The 4th International Conference on Fracture and Strength of Solid”, held at POSTECH, Pohang, Korea, August 16–18, 2000 under the auspices of Far East and Ocean Fracture Society (FEOFS)et al.     

W-Ni-Cu 和W-Ni-Fe合金的腐蚀性能

高比重钨合金是一种具有高密度,高机械强度和良好的耐腐蚀性等特性的复合材料,并广泛应用于工业和军事中。本文采用沉浸实验和电化学实验对两种钨合金(90％W-6％Ni-4％Cu和95％W-3.5％Ni-1.5％Fe)的腐蚀性能进行了研究。结果的表明,当W-Ni-Cu合金发生电偶腐蚀时,W相首先遭到腐蚀,而在W-Ni-Fe合金中,粘结相会先发生腐蚀。电动位极化测量结果表明pH值对高比重合金钨合金腐蚀速率有显著影响,与酸性环境相比较,合金在中性溶液中得到较低的腐蚀速率。根据SEM和EDX的结果分析了合金成分的溶解以及腐蚀产物的生成等腐蚀机理。     

Research on Process and Microstructure Formation of W-Ni-Fe Alloy Fabricated by Selective Laser Melting

W-Ni-Fe alloys are important materials for many practical applications; however, at present, they are usually fabricated by conventional powder metallurgy techniques, which is difficult in fabrication with complex shapes. In this work, a selective laser melting (SLM) processing method was developed for fabricating W-Ni-Fe alloys parts. A process map was obtained for selection of proper laser parameters by optimizing processing conditions. Microstructures of laser fabricated samples in different laser energy inputs were investigated. There are two coexisting forming mechanisms in the SLM process: (i) liquid phase sintering (LPS) with full melting of Ni and Fe powders but non-melting of W powders and (ii) melting/solidification with full melting of W powders. Moreover, with increasing laser energy, a transition trend of forming mechanism from LPS to full melting/solidification can be observed.     

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。     

W-Ni-Fe合金药型罩的破甲特性

为了研究W-Ni-Fe合金药型罩的射流特征及破甲特性,对W-Ni-Fe合金药型罩进行静破甲试验,采用X射线照相系统研究W-Ni-Fe合金药型罩的射流形成能力,并对侵彻后的靶板进行宏观及微观分析。结果表明,W-Ni-Fe合金药型罩能形成高速延性射流,虽然穿深较低但破孔孔径大。靶板微观分析表明,破孔表面射流残余多且形成了高硬马氏体区。XRD结果表明,射流与钢靶相互作用剧烈,在破孔表面形成了大量Fe0.95W0.05化合物。马氏体及化合物硬质相的存在使得射流能量横向耗散严重,这是造成W-Ni-Fe合金药型罩穿深低、破孔大的主要原因     

Effects of ThO2 on the solid-state sintering behavior of W-Ni-Fe alloy

Dilatometric analyses were employed to investigate the influence of ThO₂ particles on the sintering behavior of W-Ni-Fe alloys up to 1450 °C which is below the liquid formation temperature. The activation energies were obtained by analyzing by the shift of the iso-density points as a function of the linear-heating rate. It is well known that the dominant sintering mechanism of tungsten particles is grain-boundary diffusion in the solid-state. The activation energies were 304.00-467.39 kJ/mol for W-Ni-Fe and 519.10-2949.60 kJ/mol for the thoria doped alloy, respectively. The results for the non-added alloy are in agreement with the values reported in the literature. The possibility that the much higher energies for the doped alloy reflect a retardation of sintering due to the presence of thoria particles at the surface of the tungsten is discussed.     

增材制造W-Ni-Fe系高比重合金的研究进展

金属增材制造技术是从20世纪90年代初期发展起来的一项先进制造技术,能够实现高性能复杂结构金属零件的无模具、快速、全致密近净成形。高比重W-Ni-Fe合金由于具有高密度、高强度和高塑性等特性,广泛应用于国防工业和国民经济领域。近年来,W-Ni-Fe高比重钨合金的增材制造受到了广泛关注。本文综述了国内外研究机构采用选区激光熔化(SLM)技术、激光熔化沉积(LMD)技术、选区电子束熔化(EBSM)技术和粘接剂喷射打印(BJP)技术4种增材制造技术制备W-Ni-Fe合金的研究进展,从成形工艺、成形件微观组织和力学性能等方面进行了分析,并对未来研究趋势做了预测。     

喷雾造粒预合金化W-Ni-Fe三元合金粉末及射频热等离子体致密球化研究

球形致密化的钨基（W-Ni-Fe）合金粉末对增材制造等粉末成形构件的强度等物理性能的提升具有重要意义。采用喷雾造粒和射频热等离子体高温致密球化处理的方式研究了W-Ni-Fe粉末经喷雾造粒后射频热等离子体处理对其合金粉末的形貌、孔隙等的作用效果。研究表明,经喷雾造粒后所形成的96W-2.5Ni-1.5Fe三元合金粉末显微组织结构疏松,内部中空洞较多且表面粗糙;射频热等离子体对喷雾造粒粉进行处理后其综合性能提高,球形粉表面孔洞及疏松现象有所缓解,但仍有部分颗粒表面与内部存在微孔,且致密球化后的W晶粒之间Ni、Fe相含有较高含量的W元素。     

Microstructure evolution and mechanical properties of spark plasma sintered W–Ni–Mn alloy

Tungsten heavy alloys (90W–6Ni–4Mn) were prepared through spark plasma sintering (SPS) using micron-sized W, Ni, and Mn powders without ball milling as raw materials. The effects of sintering temperature on the microstructure and mechanical properties of the 90W–6Ni–4Mn alloys were investigated. SPS technology was used to prepare 90W–6Ni–4Mn alloys with relatively high density and excellent comprehensive performance at 1150–1250 °C for 3 min. The 90W–6Ni–4Mn alloys consisted of the W phase and the γ-(Ni, Mn, and W) binding phase, and the aγerage grain size was less than 10 µm. The Rockwell hardness and bending strength of alloys first increased and then decreased with increasing sintering temperature. The best comprehensiγe performance was obtained at 1200 °C, its hardness and bending strength were HRA 68.7 and 1162.72 MPa, respectiγely.     

Direct synthesis of La9.33Si6O26 ultrafine powder via sol–gel self-combustion method

Single phase La_9.33Si₆O₂₆ ultrafine powder, as a kind of highly activated precursor to prepare medium-to-low temperature electrolyte for solid oxide fuel cells (SOFCs), has been successfully synthesized via a non-aqueous sol–gel and self-combustion approach from the starting materials: lanthanum nitrate (La(NO₃)₃·6H₂O), citric acid, ethylene glycol (EG), tetraethyl orthosilicate (TEOS) and ammonium nitrate. The details of gel's self-combustion were investigated by DTA–TG and the structural characterization of as-synthesized powder from self-combustion was performed by XRD and SEM. The results show that La_9.33Si₆O₂₆ single phase of apatite-type crystal structure can be directly synthesized by sol–gel self-combustion method without further calcinations on the condition that the molar ratio (R) of NO₃⁻ to citric acid and ethylene glycol being 6:1. Such powders composed of well-dispersed particles with an average size of 200 nm and a specific surface area of 5.54 m²/g. It can be sintered to 90% of its theoretical density at 1500 °C for 10 h, about 200 °C lower than the sintering temperature for the powder derived from traditional solid reactions. The sintered material has a thermal expansion coefficient of 9.2 × 10⁻⁶ K⁻¹ between room temperature and 800 °C.     

Formation of an amorphous phase in thermally sprayed WC-Co

A WC-Co coating was sprayed by the high-velocity oxyfuel process using a feedstock of tungsten carbide clad with cobalt. The structure of the sprayed coating was characterized by x-ray diffraction (XRD), differential scanning calorimetry (DSC), and differential thermal analysis (DTA). It was found that an amorphous phase of Co-W-C ternary alloy observed as a large, broad peak in the XRD pattern can be formed in the as-sprayed WC-Co coating. The DSC, DTA, and XRD analyses revealed that the amorphous phase crystallized at a temperature of around 873 K to metallic cobalt, Co₆W₆C, and tungsten with appreciable precipitation of free carbon. The heat treatment of as-sprayed WC-Co coating at a high temperature of 1173 K suggests that annealing at a temperature higher than about 1104 K will promote the reaction of tungsten and cobalt with carbon to form the complex carbide C₀₆W₆C.     

无磁钻铤用Cr-Mn-Ni-N系高氮钢平衡凝固相变与析出行为

借助Thermo-Calc软件对无磁钻铤用Fe-(15~25)Cr-(15~25)Mn-(0~5)Ni-(0~1)Mo-(0~1)N-(0~0.8)C多元系高氮钢在凝固和冷却过程中的相变及析出行为进行研究。使用Thermo-Calc软件中的TCFE9数据库对该钢相图的垂直截面图进行计算,分析了Cr、Mn、Ni、Mo、N及C元素对无磁钻铤用高氮钢凝固及冷却过程中相变的影响,并得到了平衡凝固相变路径图。结果表明,增加Cr、Mn含量可显著提高合金中氮的溶解度,Mo元素可以微弱提高氮的溶解度,Ni、C元素显著降低氮的溶解度。Ni、C和N含量提高可扩大单相奥氏体相区,具有稳定奥氏体的作用,Cr、Mo与Mn元素缩小单相奥氏体相区,具有稳定铁素体的作用。N元素可以促进M₂(C,N)相析出,使M₂₃C₆相析出受到抑制。Cr、Mn元素可以促进Sigma相析出,C、N元素抑制Sigma相析出。M₂₃C₆相的析出主要受C含量的影响,随着C含量的升高,M₂₃C₆相的析出温度显著升高。     

多路粉末送进激光立体成形钨合金组织凝固形态分析

钨合金因具有优异的高温性能和抗蠕变、辐射、耐磨等性能在核工业、电子、兵器工业中备受关注。采用多路粉末送进的激光立体成形方法在碳钢基体表面制备了不同组分的Wi-Ni合金材料,研究了激光工艺参数对单道单层和单道多层W-Ni合金的微观组织的影响,利用CA模型进行了W-Ni合金的枝晶生长模拟,利用能谱和SEM表征的W-Ni合金成分及微观组织进行了对比。结果表明:合适的激光立体成形(LSF)工艺参数下,通过多路元素混合可以形成不同组分的W-Ni合金,合金内部组织致密,主要由未完全溶化的钨颗粒,以及W-Ni、W-Ni-Fe的化合物组成;多层沉积后,合金形成了明显的分层结构,组织从底部W-Ni-Fe杂乱枝晶逐渐过渡到顶部W-Ni二元共存的形态;CA模型的计算表明,在熔池底部无法消除等轴晶带来的影响,与试验结果一致;W90%-Ni(质量分数)的强度达到了882 MPa。     

胎盘组织核因子-κB与妊娠并发症关系研究进展

核因子-κB（NF-κB）是一种细胞内重要的转录因子,调控包括炎症、凋亡在内多种基因的表达,在胎盘中分布广泛。本文对胎盘组织中NF-κB与先兆子痫、HELLP综合征和胎膜早破等妊娠并发症的关系研究进行综述,概括了胎盘NF-κB在这些妊娠并发症发生过程中的作用以及依赖NF-κB途径治疗相关疾病的研究进展,为胎盘相关疾病的深入研究奠定基础,为妊娠并发症疾病的诊治提供新思路。     

真空熔结镍基复合涂层的冲蚀磨损特性研究

通过真空熔结的方法,在Ｗ－Ｎｉ－Ｆｅ高比重合金表面获得一定厚度的涂层,研究了该涂层受泥浆冲蚀时冲蚀磨损率与时间、粒子冲击速度及攻角的关系,并分析了涂层的稳态冲蚀磨损率随不同ＷＣ质量分数所产生的变化。     

Effect of secondary aging on microstructure and properties of cast Al-Cu-Mg alloy

To obtain better comprehensive properties of cast Al-Cu-Mg alloys, the secondary aging (T6I6) process (including initial aging, interrupted aging and re-aging stages) was optimized by an orthogonal method. The microstructures of the optimized Al-Cu-Mg alloy were observed by means of scanning electron microscopy and transmission electron microscopy, and the properties were investigated by hardness measurements, tensile tests, exfoliation corrosion tests, and intergranular corrosion tests. Results show that the S phase and θ′ phase simultaneously exist in the T6I6 treated alloy. Appropriately increasing the temperature of the interrupted aging in the T6I6 process can improve the mechanical properties and corrosion resistance of Al-Cu-Mg alloy. The optimal comprehensive properties (tensile strength of 443.6 MPa, hardness of 161.6 HV) of the alloy are obtained by initial aging at 180 °C for 2 h, interrupted aging at 90 °C for 30 min, and re-aging at 170 °C for 4 h.

     

Characterization of phase transformation and microstructure of nano hard phase Ti（C,N）-based cermet by spark plasma sintering

By means of optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM), the process of densification, the characterization of phase transformation and the microstructure for spark plasma sintering (SPS) nano hard phase Ti(C, N)-based cermet were investigated. It is found that the spark plasma sintering (SPS) enables the nano hard phase Ti(C,N)-based cermet to densify rapidly, however, the full densification of the sintered samples can not be obtained. The rate of phase transformation is significantly quick.When being sintered at 1 200℃ for 8 min, Mo2C is completely dissolved, and TiN dissolves into TiC entirely and disappears. Above 1200℃, Ti(C,N) begins to decompose and the atoms of C and N separate from Ti(C,N) resul-ting in the generation of N2 and the graphite. Due to the denitrification and the graphitization, the density and the hardness of sintered samples are rather low. The distribution of grain size of the sample sintered at 1350℃ covers a wide range of 90-500 nm, and most of the grain size are about 200 nm. The hard phase is not of typical core-rim structure. Oxides on the surface of particles can not be fully removed and present in sample as titanium oxide TiO2.Graphite exists in band-like shape.     

Microstructure characterization of W-Ni-Fe heavy alloys with optimized metallographic preparation method

Tungsten heavy alloys (WHA) have been widely adopted in many engineering applications due to their excellent physicochemical properties. Microstructure characterization is a very powerful method ranging from testing materials properties to detecting material failures and defects. However, the microstructure of WHA was not well characterized with the sample prepared by conventional method of etching with strong acids, bases or oxidant after polishing for the coarse surface. To solve the problem, the exact characterization of W-Ni-Fe heavy alloys microstructure was conducted using the sample prepared by optimized polishing method. A series of experiments were conducted to find the suitable polishing conditions including polishing pad, abrasive slurry and slurry pH. The results show that a smooth and clear microstructure sample was obtained by polishing with alkaline colloidal silica and IC polishing pad, which contained few defects compared with that obtained by conventional method of etching after polishing. The microstructure of W-Ni-Fe heavy alloys was analyzed by XRD, EDS tests and EPMA detection. The slipping phenomenon was observed in nanoindentation test using the prepared sample for the first time and the mechanism of satisfactory microstructure sample preparation was illustrated.     

Electroless deposition and characterization of Ni-P-WC composite alloys

A composite coating Ni-P-WC was produced using an electroless deposition technique from citrate bath containing WC powder. The influence of plating parameters such as WC content, pH, temperature and stirring rate on the content of WC codeposited with Ni-P alloys were investigated. The maximum value of WC (50-55 V_p) codeposited can be achieved at a particle content of 20 gL^− 1 in the electrolyte, at pH 5.5-6, temperature 85-90 °C and stirring rate of 150 rpm. Surface morphology and microstructure of Ni-P-WC coatings were determined by means of SEM and X-ray diffraction. It was found that the phase structure of the solid solution cannot be varied by codeposition of WC particles in Ni-P alloys, and it only influences the growth of the crystal planes. The properties of the composite such as hardness and abrasion resistance were also examined and compared with WC free nickel deposited layer. The presence of WC particles in the deposit significantly was found to improve the hardness and abrasion resistance of composite coatings.