Enhanced sintering of an Fe-Ni-P coated composite powder prepared by electroless nickel plating

An Fe-8.2 % Ni-6.0 % P powder was prepared by electroless nickel plating on a carbonyl iron powder, where phosphorous appeared as a contaminant of the plating process. Because of the high phosphorous concentration, persistent liquid phase sintering was effective at temperatures higher than 1000 °C. The sintered microstructure was dramatically different from the conventional approaches, where a low concentration of phosphorous was added in the form of Fe₃P. Sintering the alloy at a temperature as low as 1050 °C for 30 min yielded a sintered density of 98.6% theoretical and rounded grains having an average grain size of 53 μm. The rounded grains were surrounded by a large volume fraction of intergranular (Fe,Ni)₃P phase, arising from the high phosphorous concentration, which slightly deteriorated the magnetic saturation but significantly increased the electrical resistivity of the alloy. Generally speaking, the magnetic saturation of the sintered alloy was improved with respect to the iron-phosphorus, iron-nickel, or iron-silicon alloys fabricated by powder processing.     

Formation of Fe-19 wt%Cr-9 wt%Ni Nanocrystalline Alloy with Excellent Corrosion Resistance: Phase Transition and Microstructure

In this paper, microstructure characteristics and phase transitions of Fe-19 wt%Cr-9 wt%Ni nanocrystalline alloy are comprehensively studied during the mechanical alloying and hot pressing sintering processes. Corrosion resistance of the sintered Fe-19 wt%Cr-9 wt%Ni nanocrystalline alloy samples is further analyzed. During the mechanical alloying process, Fe-19 wt%Cr-9 wt%Ni nanocrystalline alloy powders mainly composed of metastable ferrite phase are obtained after mechanical alloying for 8, 16 and 24 h, respectively. In the subsequent hot pressing sintering process, the phase transitions(from ferrite to austenite) occur from 650 to 750 °C for Fe-19 wt%Cr-9 wt%Ni alloy powders milled for 24 h. When the sintering temperature is raised to 1050 °C for 1 h, the ferrite phase has transformed into austenite phase completely, and the obtained grain size of sintered Fe-19 wt%Cr-9 wt%Ni alloy is around 40 nm. Electrochemistry test of the sintered Fe-19 wt%Cr-9 wt%Ni alloy has been operated in 0.5 mol L~(-1) H_2SO_4 solution to show the corrosion resistance properties. Results show that the sintered Fe-19 wt%Cr-9 wt%Ni alloy exhibits excellent corrosion resistance, which is proved by higher self-corrosion potential, lower self-corrosion current density and larger capacitive reactance, compared with that of commercial 304 stainless steel.     

Effects of Al2O3 addition on the microstructure and properties of Ni activated sintered W matrix composites

In the present investigation, fabrication of high dense (> 97.8%) W matrix composites with increased microhardness values were investigated. W and W–1 wt.% Ni powders were mechanical alloyed for 18 h and sintered at 1400 °C for 1 h under Ar, H₂ gas flowing conditions in order to investigate the effects of 1 wt.% Ni addition on the densification and properties of W. The effects of Al₂O₃ particles additions on the microstructural and physical properties of the sintered W–1 wt.% Ni sample were investigated. A 92.59% relative density value of the sintered W sample increased to 99.47% with the addition of 1 wt.% Ni. Moreover, despite the observed grain growth, microhardness values significantly increased from 2.81 ± 0.34 GPa to 4.07 ± 0.16 GPa with the addition of 1 wt.% Ni. The relative density values of the sintered W–1 wt.% Ni sample slightly decreased with increasing Al₂O₃ additions, a relative density value of 97.81% was measured for the W–1 wt.% Ni sample reinforced with 2 wt.% Al₂O₃ particles. As the average grain size of W in the sintered W–1 wt.% Ni sample decreased from 4.41 ± 1.71 μm to 1.29 ± 0.39 μm with the addition of 2 wt.% Al₂O₃ particles, the microhardness of the sample increased to 5.98 ± 0.31 GPa.     

Powder injection molding of Fe-Ni soft magnetic alloys

With miniaturization and complication of the shape of electronic devices in recent years, powder injection molding (PIM) seems to be a suitable process for fabricating the higher performance soft magnetic components. In this paper, high quality Fe-50Ni soft magnetic alloy was fabricated by PIM with carbonyl iron and nickel, and the effect of sintering process on its microstructure and magnetic properties were investigated. The mechanical and magnetic properties can be obviously improved by increasing the sintering temperature or using the hydrogen atmosphere instead of high vacuum, which causes by the increase of grain size and the densification. At the optimum sintering conditions, the PIM Fe-50Ni soft magnetic alloy with high properties are obtained, whose relative density, tensile strength, Bm, Hc,μm are 97%, 465MPa,1.52T, 16.62 A·m-1 , 42.5 mH·m-1 , respectively.     

预合金粉对粉末冶金NiFe18.5Al25合金性能的影响

将元素Ni、Fe和Al粉以摩尔比56.5-18.5-25配料,分别按元素粉末高能球磨(300 r/min, 12 h)、元素粉末直接干混、50%元素粉+50%预合金粉末干混3种方式混料;混料在500 MPa的压力下压制成形,1 280 ℃下烧结;对合金烧结态进行相对密度测定、力学性能检测、X射线衍射分析(XRD)和断口形貌观察.结果表明:50%元素粉+50%预合金粉制备的合金性能最好,密度可达到6.61 g/cm3(相对密度94.8%),烧结态抗拉强度可达到868 MPa,说明元素粉末中添加的预合金粉可以控制烧结过程,提高合金的烧结密度,同时增强合金的力学性能.     

Effect of additions of zinc stearate on the properties of sintered Nd-Fe-B magnets

Zinc stearate additions have been used to increase the remanence of sintered Nd-Fe-B magnets produced by the powder metallurgy without powder pressing. Zinc stearate acts as an internal lubricant, i.e., it decreases the friction forces between the particles and favors an increase in the degree of texture of the powders, which is induced by the magnetic field. It is shown that the density and the magnetic hysteresis characteristics of sintered magnets produced using additions of 0.15 wt % zinc stearate exceeds the corresponding values obtained for magnets produced without this addition at a filling density of powders in containers of more than 2.9 and 3.0 g/cm³ in dry and wet states, respectively. Using additions of zinc stearate in the amount of 0.15% with respect to the weight of the powder, magnets with a density of 7.55 g/cm³, B _r = 14.02 kG, H _c = 7.91 kOe, and (BH)_max = 46.1 MG Oe have been produced.     

Investigation on addition of talc on sintering behavior and mechanical properties of B4C

The effect of high alumina talc powder as a sintering aid on densification of boron carbide powder was investigated. The in situ reaction of talc with boron carbide generate SiC, MgB₂, and alumina, which all aid the sintering process and permit pressureless sintering at temperatures between 2050 and 2150°C. The microstructure-property relationship has been studied in the B₄C-talc system for talc content between 0 and 30 wt.%. It became clear the addition of talc powder has a significant effect on the sintering behavior of B₄C. B₄C composites along with talc powder additions were sintered up to 98% of theoretical density. The mechanical properties were improved over those of samples without talc addition.     

激光烧结工艺参数对Fe-16%Ni合金致密度的影响

采用激光烧结成形技术研究了不同工艺参数对Fe-16%Ni金属粉末选区激光烧结成型件微观结构和致密性的影响。结果表明,随着脉冲宽度、扫描速度和铺粉厚度的增加,烧结后试样的密度先增加然后减少,随着扫描间距的增加,烧结后试样的密度减小。当脉冲宽度0.7 ms,扫描速度1000 mm/min,铺粉厚度0.15 mm,扫描间距0.15 mm时,烧结成型件成型质量较好。     

Improving the uniformity in mechanical properties of a sintered Ti compact using a trace amount of internal lubricant

Large sintered powder compacts are likely to be associated with variability in mechanical properties; an improvement of the uniformity of the mechanical properties of sintered powder compacts is important for powder metallurgy. In this work 0.3–1 wt.% stearic acid (SA) or magnesium stearate (MgSt) was added to a 40 mm diameter Ti powder compacts with height to depth (H/D) ratio of unity to give a more uniform green density. Tensile test pieces were cut from selected positions in each sintered compact to obtain the distribution of mechanical properties. Results revealed that variations in mechanical properties are due to the pore morphology with respect to size, aspect ratio and preferred orientation. A trace amount of lubricant significantly improves the uniformity in mechanical properties by optimizing the porosity distribution and minimizing the pore size and aspect ratio of pores after sintering. Such an effect was achieved by reducing the initial green density inhomogeneity and the stress induced by the mismatch of sintering shrinkage. However a relatively high 1 wt.% SA addition with a large particle size created burnt-off pores in the top and bottom zones. MgSt is not recommended since it significantly increases the oxygen content. An addition of 0.6 wt.% SA is the best choice due to the even pore distribution, small pore size and acceptable level of oxygen pick up.     

铬对FeNiMoCu系预合金粉末烧结性能的影响

将Cr以铬铁的形式加入到FeNiMoCu系预合金粉末中,经充分混合后单轴600MPa下压制,然后分别采用冷压烧结、烧结热锻和复烧工艺,研究铬对FeNiMoCu系预合金粉末烧结密度、组织及性能的影响.实验结果表明,添加到预合金粉末中的铬在1573K温度烧结时可均匀扩散到组织中,使组织性能得到改善;随添加的铬量和复烧温度的提高,微观组织硬度和表观硬度逐渐增加,经热锻及热锻复烧可获得较高的烧结密度和硬度.当复烧温度为1573K时,Fe-1.5Cr-2.0Ni-0.85Mo-1.7Cu-0.5C获得的密度为7.71 g/cm3,硬度为105HRB;Fe-4.0Cr-3.0Ni-0.85Mo-1.7Cu-0.5C获得的密度为7.63g/cm3,硬度为105HRB.     

Thermal stability and magnetic saturation of annealed nickel-tungsten and tungsten milled powders

Crystal structures, microstructures and magnetic saturation of annealed pure W powder along with W-40 wt.% Ni powder mixtures processed by high-energy ball milling were investigated using XRD, DTA, SEM and saturation magnetization techniques. Thermally induced transformations occurred at low temperature annealing. Supersaturated metastable Ni(W) solid solution formed during mechanical milling decomposed during annealing treatment into FCC Ni-rich, FCC W-rich phases and an eta-type phase which was constituted of BCC lattice of W enveloped by two FCC lattices of Ni and W. The structures of the major annealing products were close to Ni₁₀W and W₃Ni₂. The magnetic saturation of the milled W powder and W-Ni mixtures decreased with the increase in annealing temperature. Milling time was more influential on the magnetic properties of the annealed pure W powders.     

Synthesis of nano-sized Fe–Ni powder by chemical process for magnetic applications

Synthesis of nano-sized Fe–Ni permalloy of the composition 20 wt% Fe and 80 wt% Ni took place by electroless chemical reduction method in alkaline tartarate bath using hypophosphite as a reducing agent. The powder was cold compacted at 600 MPa and then sintered at 1050 °C. Metallographic investigations were performed by optical microscope and SEM with EDAX analysis. Hot-stage XRD was performed for the investigated materials to follow the phase transformations in the material. Physical, magnetic and electrical properties were studied for the prepared powder and its related sintered compacts. FeNi powder prepared from the experiments has a 200 nm particle size with 2.4 wt% phosphorus content. The prepared powder has amorphous structure with a low saturation induction (B_s) but by raising the temperature to 500 °C, the FeNi₃ intermetallic appears first and then the cubic FeNi solid solution is formed at 1050 °C, which has the highest saturation induction value.After cold compaction and sintering, the electrical conductivity and the saturation induction increased by increasing the time of sintering but the coercive force decreased and the material becomes softer after sintering. Measurements of the magnetic permeability indicate that the optimum applying field for the investigated sintered material is between 40 and 100 Oe which gives the highest range of the magnetic permeability. From the magneto-resistance measurements, it is shown that the sintered material has a positive magneto-resistance in the field direction but a negative one in the direction perpendicular to the current and the field.     

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.     

Preparation and properties of ultra-fine TiCN matrix cermets by vacuum microwave sintering

Ultra-fine titanium carbonitride (TiCN) matrix materials with a grain size less than 1 μm were successfully prepared by vacuum microwave sintering. The milling process for raw TiCN particles and the microstructure and properties of cermets produced with a composition of 15wt.%WC-17wt.%(Co+Ni)-9wt.%Mo₂C-59wt.%Ti_0.7N_0.3 and sintered by vacuum microwave were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that a ball-to-powder mass ratio of 8:1 and a milling time of 50 h provided appropriate conditions for the production of ultra-fine TiCN solid solution powders. The use of vacuum microwave sintering produced cermets with much finer grain and black core structures and higher relative density and hardness than those produced by vacuum sintering technology.     

磷元素对铜基金属粉末选区激光烧结作用机理

对不同CuP含量的多组分铜基金属粉末(Cu-CuSn-CuP)进行了选区激光烧结实验。利用X射线衍射和扫描电镜研究了添加元素P对烧结致密度及显微组织的影响。研究表明:P元素能在烧结过程中充当脱氧剂而与Cu反应生成CuPO3;但当P过量时,则会因熔体过热倾向明显而加剧氧化;适量增加P元素能改善烧结件层间结合性;而P元素过量则会因生成过多磷渣而降低润湿性及致密度;P元素亦能充当稀释剂而降低熔体粘度及表面张力,从而改善烧结致密度及组织均匀性;但若P元素过量时,则会因熔体粘度过低而导致球化现象。实验结果证实,该组铜基金属粉末体系中CuP的最佳含量为15%。     

Effect of Mo2C additions on the properties of SPS manufactured WC–TiC–Ni cemented carbides

The effect of spark plasma sintering (SPS) on the microstructure and mechanical properties of WC–Co and WC–Ni cemented carbides was studied, and compared to WC–Co produced by liquid phase sintering (LPS). There were finer WC grains with larger Co pools in the spark plasma sintered WC–Co, resulting in higher hardness and slightly lower fracture toughness than the liquid phase sintered WC–Co. The influence of the addition of 0.5–5 wt.%Mo₂C to WC-based cemented carbide containing 6.25 wt.%TiC and 9.3 wt.%Ni prepared by SPS was also studied. This addition improved the wettability between WC and Ni and lead to the improvements of microstructures, resulting in good combinations of hardness, fracture toughness and modulus of elasticity that were comparable to WC–Co based cemented carbides.     

Electrochemical behavior of sintered oxide dispersion strengthened stainless steels

The electrochemical behavior of powder metallurgy (P/M) oxide dispersion strengthened stainless steels (SS) (316L and 434L) have been compared with standard 430 and 316 wrought samples in 0.05 mol/l sulfuric acid. The effects of sintering temperature and yttria addition on the electrochemical behavior have been studied. The behaviour of the dispersion strengthened SS was comparable to that of the straight P/M samples. The straight P/M samples sintered at 1400 °C exhibited better corrosion resistance compared to the samples sintered at 1250 °C and this has been correlated to sintered densities. The P/M austenitic SS were superior to the P/M ferritic SS. Pitting resistance, studied by cyclic polarization experiments in 3.56 wt.% NaCl, of the P/M samples were comparable to the wrought samples. The addition of Y₂O₃ did not affect the pitting resistance.     

Effects of Y2O3 additions on mechanically alloyed and sintered W—4 wt.% SiC composites

In this study, the effect of Y₂O₃ additions on the microstructural and the physical properties of W-SiC composites was investigated. Powder blends of W—4 wt.% SiC, W—4 wt.% SiC—1 wt.% Y₂O₃ and W—4 wt.% SiC—5 wt.% Y₂O₃ were mechanically alloyed (MA'd) using a Spex mill for 24 h. MA'd composite powders were sintered under inert Ar and reducing H₂ gas conditions at 1680 °C for 1 h. Microstructural and morphological characterizations of composite powders and sintered samples were carried out via SEM and XRD analyses. Furthermore, density measurements and hardness measurements of sintered samples were carried out. A highest Vickers microhardness value of 11.4 GPa was measured for the sintered W—4 wt.% SiC—5 wt.% Y₂O₃ while W—4 wt.% SiC sample possessed the highest relative density value of 97.7%.     

Effect of carbon on the coefficient of thermal expansion of as-cast Fe−30wt.%Ni−12.5wt.%Co−×C invar alloys

The segregation (distribution) of nickel and the composition of its constituents influence the low thermal expansion characteristics (Invar effect) in Fe?30 wt.% Ni?12.5wt.% Co?×C Invar alloy. The change of coefficient of the thermal expansion and magnetic properties were studied as an aspect of carbon addition causing the segregation of Ni in primary austenite of as-cast Fe?30wt.% Ni?12.5wt.% Co Invar alloy. The coefficient of thermal expansion of Fe?30 wt.% Ni?12.5 wt.% Co?×C Invar alloy showed its lowest value at 0.08 wt.% carbon, increased with increasing carbon content in the range of 0.08–1.0 wt.%C, kept constant at 1.0–2.0 wt.%C and decreased at carbon higher than 2.0 wt.%. The effective distribution of the coefficient of nickel in as-cast Fe?30 wt.% Ni?12.5 wt.% Co?×C Invar alloy increased with increasing carbon content. The volume fraction of the γ phase of Fe?30 wt.% Ni?12.5 wt.% Co?×C alloy increased with increasing carbon content. The microstructure of Fe?30 wt.% Ni?12.5 wt.% Co?×C alloy changed with the carbon content was independent of the coefficient of thermal expansion. The Curie temperature changed linearly with the carbon content and was similar to the change of the coefficient of thermal expansion. Moreover, the coefficient of thermal expansion decreased when the ratio of saturation magnetization to Curie temperature (σ_s/T_c) increased, decreasing the Curie temperature and showed a specific relationship with the magnetic properties of the Fe?30 wt.% Ni?12.5 wt.% Co?×C Invar alloy.     

Low-temperature sintering method for NiCuZn ferrite and effect of Mn addition on electromagnetic properties

Low temperature sintering NiCuZn ferrite was employed at most cases due to its co-firability with Ag （below 960 ℃）. The NiCuZn ferrite sintered body with high-strength and high-frequency magnetic properties was fabricated. Firstly, NiCuZn ferrite powder was synthesized under CO2 atmosphere at 500 ℃from the mixed doxalate synthesized by liquid phase precipitation method. Then a small amount of boric acid （H3BO3） was added to the powder, and the NiCuZn ferrite powder compact was prepared with Newton press and CIP methods. Finally, NiCuZn ferrite sintered body was fabricated by sintering at 900 ℃ under CO2 atmosphere. The minimum sintering temperature （800 ℃） was determined by the study of high temperature shrinkage. By this method, NiCuZn ferrite sintered body with 0.5% （mass fraction） boric acid was obtained, which has the bending strength of 340 MPa. The effect of various Mn addition on electromagnetic properties were studied.