Selective Laser Melting Process of Fe-Ni Metal Powder

The density of the SLM forming parts is investigated to determine the good technological parameters of SLM at the same time obtain the dense parts. In the SLM experiment, material used is Fe-Ni metal powder, the good technological parameters of SLM are determined by analyzing the effect of the laser electric current, the laser pulse width, the pulse of laser light frequency, the scan speed, the scan interval, push powder thickness and the scanning way on the single channel scanning, the single-layer scannin...     

Fe-Ni系金属粉末选区激光熔化成型工艺研究

选区激光熔化(SLM)技术可用于金属粉末快速制作冶金实体,成型件致密性是SLM工艺研究的重点,也是制备金属制件的基本要求.选用铁镍系金属粉末,在不同的激光功率、扫描速度和铺粉厚度等工艺参数条件下,采用单道扫描和多层单道扫描等方式进行实验,并利用扫描电镜对不同工艺所制备的试样进行微观形貌研究和致密性分析,确定了优化的工艺参数匹配并制备出块体试样,致密度达80％以上.     

Laser operated borate polymer nanocomposites

We have found that UV polarized treatment of the nanocrystals (non-centrosymmetric Li₂B₄O₇ and centrosymmetric α-BaB₂O₄) embedded into the olygoether acrylate photopolymer samples cause substantially different response depending on the laser features. For the Li₂B₄O₇ NC, during treatment by pulsed 7 ns laser polarized nitrogen laser pulses at 337 nm we observed substantial red spectral shift of the energy gap from 7.3 eV up to 6.3 eV. The spectral shift is disappeared during the 15 min after the interruption of optical treatment. The effect exists only in the nanocrystallites with sizes below 200 nm. At the same time for the centrosymmetrical α-BaB₂O₄ nanocrystallites this effect was absent. However the photoinduced second order optical effects induced by coherent bicolor treatment by wavelengths 532 nm and 266 nm are enhanced for the α-BaB₂O₄ NC and are absent for the Li₂B₄O₇ ones.     

Laser sintering of ultradispersed iron-base powder materials

Experimental data on the formation of the structure and mechanical properties of layers produced from ultradispersed Fe-base powder mixtures under laser irradiation (λ ∼ 1 μm) with a radiation density q ∼ 10³ W/cm² and pulse duration 10⁻⁵ s are reported. The results of the study provide a background for the development of a method of producing complex metal alloys in a metastable condition with the help of high-concentration energy sources. The field of application of this method is the production of thin layers on the surface of highly loaded friction units.     

Fe-C混合粉末激光烧结成形试验

在激光选区成形机上对一定比例的、未添加低熔点粘结剂Fe-C混合粉末进行了烧结工艺试验研究,分析了工艺参数对金属粉末烧结成形的影响,分析了激光功率、扫描间隔、扫描速度与烧结层厚的关系,建立了扫描间隔与烧结层厚之间的关系公式并由试验数据给予了论证.通过烧结件微观结构分析了Fe-C粉末在激光作用下的烧结机制及烧结过程出现的球化现象.获取了合理的烧结工艺参数并烧结出具有一定精度、致密性和复杂的Fe-C金属件.     

Laser polishing of parts built up by selective laser sintering

In this work, a surface finish method for parts built-up by selective laser sintering (SLS) is presented. One of the main drawbacks of the SLS technique is the high surface roughness of resulting parts. Therefore, parts have to be polished to be valid for operation conditions. Polishing processes are usually based on manual abrasive techniques. However, in the present paper, a surface polishing method based on laser irradiation is presented. The laser beam melts a microscopic layer on the surface, which re-solidifies under shielding gas protective conditions, resulting in a smoother surface.Laser-polishing tests for lines, planar surfaces and inclined planes have been performed, with satisfactory results in all the cases. The experimental tests were carried out on sintered test parts with an initial roughness of 7.5–7.8 μm Ra. The tested material is a commercial alloy denominated LaserForm ST-100^©, composed by sintered stainless steel and infiltrated bronze that it is used mainly for the constitution of injection moulds. Experimental results present final surface roughness below 1.49 μm Ra, which represent an 80.1% reduction of the mean roughness. Finally, a complete analysis of test probes and its metallurgical composition is presented. Considering that the material presents a non-homogeneous structure, the polished surfaces present slightly higher hardness values and are more homogeneous than the initial ones. Thus, polished surfaces do not present any heat affected zone or cracks, which could cause failure during the part operation.     

Fabrication and mechanical properties of WC-Co-Al2O3 nanocomposites by spark plasma sintering

Small amounts of nanocrystalline Al2O3 particles were doped in WC-Co nanocrystalline powders to study their reinforcing effects, and spark plasma sintering technique was used to fabricate the WC-Co-Al2O3 nanocomposites. Experimental results show that the use of Al2O3 nanoparticles as dispersions to reinforce WC-Co composites can increase the hardness, especially the transverse rupture strength of the WC-Co hardmetal. With addition of 0.5%(mass fraction) Al2O3 nanoparticles, the spark plasma sintered WC-TCo-0. 5Al2O3 nanocomposites exhibit hardness of 21.22 GPa and transverse rupture strength of 3 548 MPa. The fracture surface of the WC-TCo-0.5Al2O3 nanocomposites mainly fracture with transcrystalline rupture mode. The reinforcing mechanism is maybe related to the hindrance effect of microcracks propagation and the pinning effect for the dislocations movement, as well as the residual compressive strength due to the Al2O3 nanoparticles doped.     

Microstructure and properties of alumina-silicon carbide nanocomposites fabricated by pressureless sintering and post hot-isostatic pressing

Al₂O₃/5%SiC nanocomposites were fabricated by pressureless sintering using MgO as a sintering aid and then post hot-isostatic pressed (HIP), which can subsequently break through the disadvantage of hot-pressing process. The MgO additive was able to promote the densification of the composites, but could not induce the grain growth of Al₂O₃ matrix due to the grain growth inhibition by nano-sized SiC particles. After HIP treatment, Al₂O₃/SiC nanocomposites achieved full densification and homogeneous distribution of nano-sized SiC particles. Moreover, the fracture morphology of HIP treated specimens was identical with that of the hot-pressed Al₂O₃/SiC nanocomposites showing complete transgranular fracture. Consequently, high fracture strength of 1 GPa was achieved for the Al₂O₃/5%SiC nanocomposites by pressureless sintering and post HIP process.     

Microstructure and properties of alumina-silicon carbide nanocomposites fabricated by pressureless sintering and post hot-isostatic pressing

Al2O3/5%SiC nanocomposites were fabricated by pressureless sintering using MgO as a sintering aid and then post hot-isostatic pressed (HIP), which can subsequently break through the disadvantage of hot-pressing process. The MgO additive was able to promote the densification of the composites, but could not induce the grain growth of Al2O3 matrix due to the grain growth inhibition by nano-sized SiC particles. After HIP treatment, Al2O3/SiC nanocomposites achieved full densification and homogeneous distribution of nano-sized SiC particles. Moreover, the fracture morphology of HIP treated specimens was identical with that of the hot-pressed Al2O3/SiC nanocomposites showing complete transgranular fracture. Consequently, high fracture strength of 1 GPa was achieved for the Al2O3/5%SiC nanocomposites by pressureless sintering and post HIP process.     

Effect of sintering techniques on the microstructure and tensile properties of nano-yttria particulates reinforced magnesium nanocomposites

In the present study, magnesium nanocomposites were fabricated using magnesium as matrix and nano-yttria as reinforcement. Nanocomposites with 0.2 and 0.7 vol.% of Y₂O₃ particulates with an average size of 29-50 nm were synthesized blend-press-sinter powder metallurgy technique followed by hot extrusion. Conventional slow heating and microwave assisted rapid heating sintering techniques were used. Microstructural characterization of the materials revealed fairly uniform distribution of reinforcement with the presence of minimal porosity in all of the processed materials, while significant grain refinement in the cases of conventionally sintered materials. Tensile properties characterization of the conventional and microwave sintered nanocomposites revealed that significant and resembling increase in the 0.2% yield strength and ultimate tensile strength of magnesium matrix with the increasing presence of reinforcement. The ductility and work of fracture of magnesium matrix increased significantly in the case of conventionally sintered nanocomposites when compared to the microwave assisted sintered nanocomposites.     

Noncollinear magnetism of Fe-rich Fe-Ni alloys

The magnetic structure of Fe-rich FeNi alloys has long been a subject of great scientific interest and controversy. In this study, the authors attempt to understand an interesting phenomenon that the average magnetic moment of the alloys in the γ-phase (fcc) decreases dramatically in the composition range near 70% Fe. Although the observation was made more than 30 years ago, the nature of the mechanism for this moment collapse is still controversial. In this approach, the noncollinear locally self-consistent multiple-scattering (LSMS) method is applied to the magnetic structure calculation of large unit cell samples consisting of Fe and Ni atoms. The Fe and Ni atoms are randomly distributed on a fcc lattice. The moment directions are initialized to be randomly oriented and then, as the self-consistent iterations proceed, are allowed to rotate to minimize the total energy. Astable magnetic structure of the alloy is determined by the final moment configuration. Results are compared with experiments and the possible existence of noncollinear magnetic structures are discussed.     

开孔泡沫Fe-Ni的电磁屏蔽性能

利用专利技术制备了开孔泡沫Fe-Ni材料,并对其电磁屏蔽效能进行了研究。结果表明,在0.03～1500MHz的频率范围内,开孔泡沫Fe-Ni的屏蔽效能在60～85dB之间,屏蔽效能良好;而在0.03～400MHz范围内,其屏蔽效能与铝合金板的屏蔽效能相当。开孔泡沫Fe-Ni的电磁屏蔽效能主要受泡沫结构的影响,随着开孔孔径以及泡沫体孔隙率的减小其电磁屏蔽效能增加显著。而当材料的孔径以及厚度一定时,泡沫体孔隙率的变化对电磁屏蔽效能的影响较其他因素小。     

The Fe-Ni (iron-nickel) system

The online version of the original article can be found at     

Effect of tungsten carbide nanoparticles on mechanical properties and sinterability of B4C-WC nanocomposites using pressureless sintering method

The effect of tungsten carbide (WC) nanoparticles on sinterability and mechanical properties of boron carbide is investigated in this study. Boron carbide, being one of the hardest materials nowadays, has a variety of applications in wear-resistant components such as cutting tools. The low strength and low fracture toughness property of this material is the drawback in its application. Production of high density boron carbide is a problem due to its covalent bonds, low plasticity, surface energy and self-diffusion ratio, high resistance to slide in the grain boundaries etc… Boron carbide samples containing 5,10,20 and 30 vol.% WC were manufactured by firstly cold press and then sintering at three elevated temperatures of 2150 °C, 2200 °C and 2250 °C. It observed that addition of WC nanoparticles results in increase in mechanical properties and density of boron carbide. The highest increase is in the 30 vol.% sample with sintering temperature of 2250 °C were the density is improved by 23%, hardness by 33%, Young's modulus by 53%, and fracture toughness by 38% compared to pure boron carbide.     

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.     

Rolling and recrystallization textures in Fe-Ni alloys

The texture evolution of Fe base Fe-Ni alloys was systematically investigated for various processing parameters. The hot bands consisted of recryslallized grains and revealed diffuse textures except for the center layer where a weak cube component developed. The cold rolling texture development was characterized. regardless of Ni content, such that the orientation densities of the texture components belonging to the β-fibre were nearly similar for a given rolling reduction and systematically increased with rolling reduction On annealing the Cube component dominated the recrystallization texture, and its orientation density depended on cold rolling reduction. These characteristics of the texture development is similar to those of pure copper. The similarity of the texture evolution in Fe-Ni alloys and pure copper is attributed to the fact that they have commonly medium stacking fault energies