Influences of sub-micrometer Ta and Co dopants on microstructure and properties of tungsten heavy alloys

Tungsten heavy alloys are aggregates of particles of tungsten bonded with Ni/Fe or Ni/Cu via liquidphase sintering. The sub-micrometer Ta Co powder was added to this aggregate to strengthen the bonding phase. It is found that the main fracture pattern of the alloys is cleavage of tungsten grains and ductile rupture of bond phase,leading to improved tensile strength and elongation. Dopant Ta can act as grain size inhibitor in tungsten heavy alloys.     

Distribution of Phosphorus and Its Effects on Precipitation Behaviors and Tensile Properties of IN718C Cast Superalloy

The effect of phosphorus on the precipitations of γ",γ' and δ phases and associated tensile properties in IN718C alloy are investigated in this study.It is revealed that P atoms are dissolved in the grain interior to a relatively high degree and hence influence the precipitation behaviors in the grain interior and improve the tensile strength of IN718C alloy.γ" and γ' phases did not precipitate in the alloy without P addition during air cooling,while γ" and γ' phases precipitated in the grain interior during air cooling in the alloys with P addition,and the amounts of γ" and γ' phases increased with increasing P content.Therefore,the Vickers micro-hardness in the as-cast state increased gradually with increasing P content.In double-aging state,the sizes of γ" and γ' phases in the alloys with P addition were larger than that in the alloy without P addition,while the sizes were invariable when the P content(wt%)was higher than 0.015.Therefore,the micro-hardness and tensile strength of IN718C alloy treated by double aging increased first and then kept invariable with increasing P content.The precipitations of δ phases both in the grain interior and on grain boundaries were inhibited by P markedly.The inhibitory effect of P on δ phase enhanced gradually with increasing content of P,but the plasticity increased first and then decreased.What is more,the crack tended to propagate into the matrix around the particles(Laves phases and NbC carbides)in the alloys without P addition at the beginning of the tensile fracture,while it tended to propagate along the interfaces between the matrix and those particles in the alloys with P addition,which resulted from the synthetical effect of P on γ" γ' and δ phases.     

Structural and magnetic properties of Sm2Fe17-xNbx （x = 0-4） alloys prepared by HDDR processes and their nitrides

Sm2Fe17-xNbx （x = 0-4） powder was synthesized by HDDR treatment and nitrogenation. The effects of partial Nb substitution for Fe on the structural and magnetic properties of Sm2Fe17-xNbx alloys and their nitlides were investigated. It was seen that Sm2（Fe,Nb）17 phase exists in both annealed and HDDR-treated Sm2Fe17-xNbx alloys. However, its content is decreased with the increase in Nb substitution. In annealed alloys, Sm2（Fe,Nb）17 phase becomes unstable and will dissociate into SmFe2 and Fe-rich phases when x 〉 1.5. With HDDR-treatment, the Nb concentration in recombined Sm2（Fe,Nb）17 phase is decreased, and the content of Fe-rich phases is increased. Sm2Fe17-xNbx powder exhibits dendritic cracks and fine particles with a size of less than 300 nm. In nitrogenated alloys, N atoms mainly enter 2：17-type phase to form Sm2（Fe,Nb）17Ny. Partial Nb atoms in Sm2（Fe,Nb）17Ny phase will be released or excluded by nitrogen atoms. Fe-rich phases increase, and are followed by the amorphous Sm2（Fe,Nb）17Ny phase. Nb substitution for Fe with x = 0.5 and 1.0 in Sm2Fe17-xNbxNy powders increases the coercivity and remanence. But when x is greater than 2.0, Nb substitution will deteriorate the magnetic properties.     

Microstructure and hardness of binary Cr-Ta alloys

The dependances of the microstructure and hardness of the binary Cr-Ta alloys [ Cr-9.0, -9.2, -9.4, -9.6,-9.8, and -13.0 Ta] (mole fraction, %) were investigated. When Ta content of the alloy is less than 9.4%, there are primary dandrite grains of a Cr solid-solution phase existing in the matrix of Cr-Cr2Ta eutectic colonies in the alloy. Moreover, the regular polygon grains of the primary Cr2Ta Laves-phase are surrounded by the Cr-Cr2Ta eutectic colony in the hyper-euteetic Cr-9.4 96 Ta alloys. The scanning electron microphotograph shows that one of the Cr2Ta phase plates of an eutectic colony always connects with the primary Cr2Ta Laves-phase grain in a hyper-eutectic alloy. The eutectic colony size of Cr-Ta alloys decreases with increasing Ta. In addition, the macrohardness of Cr-Ta alloys is influanced by the chemical composition at room temperature. The binary eutectic Cr-Ta alloy presents the lowest hardness on a macrohardness scale.     

Solid solubility extension and microstructure evolution of cast zirconium yttrium alloy

Yttrium addition can improve the oxidation resistance,mitigate hydrogen embrittlement and thus enhance the mechanical properties of the zirconium alloy.To study solid solubility extension of yttrium in zirconium alloy,the lattice parameters of a-Zr phase in Zr–Y alloy were accurately determined by X-ray diffraction(XRD).Yttrium exhibits solid solubility extension in the cast zirconium alloy which forms a metastable supersaturated solid solution with solubility limit of around 3 wt%.The effect of yttrium and thermal treatment on the microstructure of the alloys was investigated by optical microscopy(OM)and scanning electron microscope(SEM).The cast Zr–Y alloy shows a normal polycrystalline structure with dispersed a-Y particles when Y content is lower than 4 wt%,while the alloy shows a eutectic structure with dendrites formation when the Y content is higher.Yttrium exhibits a strong grain refining effect on zirconium alloy and precipitates from the metastable supersaturated Zr matrix after annealing at 700 and 900 °C.     

Effect of Ca on microstructure and high temperature creep properties of AM60-1Ce alloy

A series of AM60-1Ce-xCa(x=0, 0.5, 1.5, 2.5) magnesium alloys were prepared by gravity casting method and analyzed by means of XRD, DSC and SEM. The effects of Ca on normal temperature mechanical properties and high temperature creep behavior of alloys were characterized by tensile and constant creep test.Microstructure analysis indicated that Ca was preferentially combined with Al in the alloy to form the high melting point Al_2Ca phase at the grain boundary. The addition of Ca can refine the crystal grains and reduces the content of β-Mg_(17)Al_(12) phase. With the increase of Ca content in the alloy, Al_2Ca phases at the grain boundary gradually changed to the network of lamellar structure, and replaced the β-Mg_(17)Al_(12) phase as the main strengthening phase gradually. The creep resistance of the alloy continuously increases because the high-temperature stable phase Al_2Ca firmly nailed at grain boundaries impedes the sliding of grain boundaries. However, when the addition of Ca was more than 1.5%, mechanical properties of the alloy started to decrease, which was probably due to the large amount of irregularly shaped Al_2Ca phases at the grain boundary. Experimental results show that the optimal addition amount of Ca is 1.5 wt.%.     

Preparation of high-purity tantalum ethoxide by vacuum distillation

Effects of reflux ratio, water addition and content of water in ethanol on the purity and yield of tantalum ethoxide during vacuum distillation were investigated under the operational conditions of pressure of 1kPa, oil bath temperature of 210-230 ℃, and outlet temperature of 190℃. The condensate sample was characterized by FTIR, 1↑H-NMR spectroscopy and Raman spectra, respectively. The contents of tantalum, carbon and hydrogen in the sample were also determined with elemental analysis instrument. The obtained results consistently demonstrate that the condensate is tantalum ethoxide. The content of impurity, such as Al, As, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, Pb, Sn, Ti, V and Zn, in tantalum ethoxide is less than 0.000 05%, while Nb content is less than 0.000 5%. The content of impurities in tantalum ethoxide sample excels that of Epichem Group＇s requirement for Ta（OC2H5）5 of 99.999%.     

Microstructure and mechanical properties of Mg-xLi-3Al-1 Ce alloys

Several Mg-xLi-3Al-lCe alloys were prepared by vacuum induction heating. These alloys are Mg-5Li-3Al-lCe, Mg-8Li-3Al-lCe and Mg-14Li-3Al-1C e, respectively. The microstructure and phase composition of these alloys were analyzed by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffractometry. The mechanical properties of these alloys were measured with tensile tester. The results show that, Mg-5Li-3Al-1Ce has a single phase （α） structure, Mg-8Li-3Al-lCe has a double phases （α＋β） structure, Mg-14Li-3Al-1Ce has a single phase （β） structure. And some compounds distribute in the matrix. After being rolled, the grain size of all the alloys is refined. Under the condition of the same content of other alloying elements, the mechanical properties of Mg-5Li-3Al-1Ce are relatively high. With increasing Li content, the strength of both as-cast and as-rolled alloy decrease. For the as-cast alloys, with increasing Li content, the elongation increases. While for the as-rolled alloys, with increasing Li content, the elongation decreases. Ce has refining effect on these alloys.     

Grain refinement and mechanism of CAl_（0.5）W_（0.5） compound in Mg-Al alloys

The effect of CAl0.5W0.5(CAW) compound on the grain refinement of Mg-Al based alloys was investigated.The results show that CAW compound is an effective and active grain refiner.The grain size of binary Mg-Al alloys is more than 500 μm,and it is changed to about 110 μm with a 1 wt.% CAW addition.The hardness increased with the decease of grain size monotonously.The mechanical properties are improved by the addition.The fine grain size is mainly ascribed to the dispersed Al2CO particles,which are very potent nucleating substrates for Mg-Al alloys.The nucleation cores formed by chemical reaction directly are well-distributed in the matrix.     

Microstructure and properties of modified and conventional 718 alloys

Continuing the effort to redesign IN718 alloy in order to provide microstructural and mechanical stability beyond 650 ℃, IN718 alloy was modified by increasing the Al, P and 13 contents, and the microstructure and mechanical properties of the modified alloy were compared with those of the conventional alloy by SEM and TEM. The precipitation of the grain boundaries of the two alloys is different. The Cr-rich phase, Laves phase and α-Cr phase are easily observed in the modified alloy. The γ＂ and γ＇ phases in the modified alloy are precipitated in a ＂compact form＂. The tensile strengths of the modified alloy at room temperature and 680 ℃ are obviously higher than those of the conventional one. The impact energy of the modified alloy is only about half of that of the conventional alloy. Ageing at 680 ℃ up to 1000 h lowers the tensile properties and impact energy of both the conventional and modified 718 alloys, except increasing the ductility at 680 ℃. It is concluded that the modified alloy is more stable than the conventional one.     

稀土Y在90W-7Ni-3Fe合金中的存在形态和分布特征

以喷雾干燥法制备的不同稀土Y含量的90W-7Ni-3Fe复合粉末为原料,在不同的烧结温度下制备出不同稀土含量的钨合金,采用XRD、SEM和EDX研究了稀土Y在90W-7Ni-3Fe合金中的存在形态和分布规律。结果表明:稀土Y以Y2O3的形式存在于合金中,且钨颗粒内部未发现稀土Y的存在。Y的添加量为0.4%时,以富Y颗粒的形式分布在钨颗粒与粘结相之间;当添加量为5%时,在粘结相中形成了富Y区域。添加稀土Y可以有效地细化钨颗粒。     

Microstructural control of and mechanical properties of mechanically alloyed tungsten heavy alloys

93W-5.6Ni-l.4Fe tungsten heavy alloys with controlled microstructures were fabricated by mechanically alloying of elemental powders of tungsten, nickel and iron by two different process routes. One was the full mechanical alloying of blended powders with a composition of 93W-5.6Ni-l.4Fe, and the other was the partial mechanical alloying of blended powders with a composition of 30W-56Ni-14Fe followed by blending with tungsten powders to form a final composition of 93W-5.6Ni-l.4Fe. The raw powders were consolidated by die compaction followed by solid state sintering at 1300°C for 1 hour in a hydrogen atmosphere. The solid state sintered tungsten heavy alloys were subsequently liquid phase sintered at 1445∼1485°C for 4-90 min. The two-step sintered tungsten heavy alloy using mechanically alloyed 93W-5.6Ni-l.4Fe powders showed tungsten particles of about 6-15 μm much finer than those of 40 um in a conventional liquid phase sintered tungsten heavy alloy. An inhomogeneous distribution of the solid solution matrix phase was obtained in the two-step sintered tungsten heavy alloy using partially mechanically alloyed powders. The two-step sintered tungsten heavy alloy using mechanically alloyed 93W-5.6Ni-l.4Fe powders showed larger elongation of 16% than that of 1% in the solid state sintered tungsten heavy alloy due to the increase in matrix volume fraction and decrease in W/W contiguity. Dynamic torsional tests of the two-step sintered tungsten heavy alloys showed reduced shear strain at maximum shear stress than did the sintered tungsten heavy alloys using the conventional liquid phase sintering.     

Effect of tungsten content on microstructure and quasi-static tensile fracture characteristics of rapidly hot-extruded W-Ni-Fe alloys

Tungsten heavy alloys (WHAs) with three different compositions (90W-7Ni-3Fe, 93W-4.9Ni-2.1Fe and 95W-3.5Ni-1.5Fe, wt.%) were heavily deformed by one-pass rapid hot extrusion at 1100 °C with an extrusion speed of ~ 100 mm/s and an extrusion ratio of ~ 3.33:1. The influence of tungsten content on the microstructure and tensile fracture characteristics of the as-extruded alloys was investigated in detail. The results show that the tungsten particles in the as-extruded 95W have the largest shape factor compared to the as-extruded 90W and 93W alloys and this implies that the tungsten particles in the as-extruded 95W alloy were subjected to the heaviest plastic deformation. In addition, ultimate tensile strength (UTS) and hardness (HRC) are significantly improved after rapid hot extrusion. The as-extruded 95W alloy processes the highest strength (1455 MPa) and hardness (HRC40) but the lowest elongation (5%), followed by the as-extruded 93W (UTS1390MPa; HRC39; 7%) and 90W alloys (UTS1260MPa; HRC36; 10%). The fracture morphology shows the distinct fracture features between the as-sintered alloys and the as-extruded alloys. For the as-sintered alloys, the fracture modes are various while transgranular cleavage of tungsten particles is the main characteristic in the as-extruded alloy. Meanwhile, the fracture modes of the three as-extruded alloys vary slightly with the tungsten content. TEM bright field images indicate that many lath-like subgrains with the width of 150-500 nm are present in the three as-extruded alloys, particularly in the as-extruded 93W and 95W alloys. Furthermore, the dislocations are absent in the γ-(Ni, Fe) phase. This means that dynamic recovery-recrystallization process took place during rapid hot extrusion.     

退火温度对挤压态细晶钨合金性能及组织演变的影响

采用稀土微合金化和液相强化烧结技术制备细晶93W-4.9Ni-2.1Fe+0.03%Y合金。研究在快速热挤压形变强化后,时效热处理对挤压态细晶93W-4.9Ni-2.1Fe+0.03%Y合金显微硬度和组织演变的影响,并与相应条件的传统钨合金进行对比。结果表明,随着退火温度的升高,2种钨合金钨相的显微硬度大大降低。EDS分析表明,随着退火温度的升高,钨合金粘结相中钨含量逐渐增加,其中细晶钨合金经过1200 ℃退火处理后,粘结相钨含量高达26.11%,而传统钨合金在1350 ℃退火处理后含量最高,达到28.14%。显微组织观察表明,退火有利于降低W-W连接度和细化钨颗粒;与传统钨合金相比,高温退火后,细晶钨合金的粘结相体积比更高且分布更为均匀     

放电等离子烧结时间对高密度W-7Ni-3Fe合金组织性能的影响

利用放电等离子烧结技术制备高密度W-7Ni-3Fe合金,研究了烧结保温时间对合金致密度、物相、显微组织以及力学性能的影响。结果表明,在1200℃烧结5~14 min后,合金均能实现充分致密化,保温时间对相对密度影响较小。合金中的W晶粒随保温时间的延长开始尺寸变化不大,烧结11 min以上才明显长大,但大多数W晶粒尺寸仍小于5μm。烧结时间超过8min,合金中新出现一种灰色的富W组织。随保温时间延长,合金的洛氏硬度下降不大,然而抗弯强度却明显上升。合金弯曲断口形貌在较短保温时间以沿晶断裂为主,粘结相的延性撕裂和W晶粒的解理断裂随烧结时间延长逐渐增多。     

On structure property correlation in high strength tungsten heavy alloys

Detailed structure-property correlation has been carried out in high strength tungsten heavy alloys. Alloys of compositions 90W-6Ni-2Fe-2Co, 89W-6Ni-2Fe-3Co, 89.5W-6Ni-2Fe-2Co-0.5Mo, 89.75W-6Ni-2Fe-2Co-0.25Mo, 90W-6Ni-1.5Fe-2.5Co and 90W-6Ni-1Fe-3Co have been prepared by liquid phase sintering followed by large deformation during thermo mechanical processing and studied for microstructure and mechanical properties. Despite differences in composition, higher volume fraction of matrix and lower W-W contiguity in the microstructure result in superior tensile strength and impact toughness. Increasing W content in the matrix enhances mechanical properties by imparting solid solution strengthening, increasing the matrix volume fraction and reducing W-W contiguity. The alloy 90W-6Ni-1Fe-3Co shows superior balance of properties with ultimate tensile strength of 1600 MPa and average impact toughness of 121 J/cm².     

Densification,microstructural evolutions of 90W-7Ni-3Fe tungsten heavy alloys during laser melting deposition process

Thin walled 90W-7Ni-3Fe tungsten heavy alloys (WHAs) have been prepared by a laser melting deposition (LMD) additive manufacturing technique using different input laser volume energy densities. Detailed investigations on densification and microstructural evolutions of the LMD process have been carried out. The result shows that the sample density increases with increasing input energy density by elimination of “lack of fusion” defects. However, some gas delivered with powders gets trapped in the molten pool due to the fast cooling rate and complex shapes of W particles, resulting in a prevalence of small round pore defects even under high input energy densities. Near full density can be obtained when the energy density reaches 74 J/mm³. The LMD WHAs have two phase microstructures consisting of polygonal or dendritic W particles embedded in a nickel‑iron matrix, which has large sized columnar grains due to epitaxial growth. The polygonal particles are partially dissolved/melted W powder particles. The dendritic particles are newly formed grains due to the reprecipitation of supersaturated W in the nickel‑iron matrix during solidification. The proportion of dendritic particles increases with the increasing input energy density. A microstructure evolution process adapted from traditional liquid phase sintering process containing three stages of rearrangement, solution-reprecipitation, and solid state is proposed for the LMD process.     

Properties and microstructural evolution of W-Ni-Fe alloy via microwave sintering

The mechanical properties and microstructure evolution of 93W-4.9Ni-2.1Fe (wt.%) alloys were investigated via microwave sintering. The microwave sintering promoted the dissolution and diffusion of tungsten atoms in the matrix phase and strengthened sintering activity. With the increase of microwave sintering temperature, pores in the alloy were reduced and gradually eliminated, tungsten grains coarsened, the distribution of tungsten grains and matrix phase became more homogeneous, and the fracture mode transformed from intergranular fracture to tungsten transgranular cleavage fracture, respectively. The W-matrix interfacial bond strength of 93W-4.9Ni-2.1Fe was enhanced and the mechanical properties were significantly improved with the increase of sintering temperature.     

STRAIN AND FRACTURE OF LIQUID PHASE SINTERED ALLOY 90W-TNi-3Fe

研究了液相烧结的90W-7Ni-3Fe合金的形变和断裂特征。试样由基体相首先开始屈服,承受塑性变形。当界面结合强度较低时,试样首先沿界面裂开,而当界面结合强度增高到高于钨的解理断裂应力时,试样同时发生钨球的穿晶解理开裂和基体相的塑性撕裂。 氢是造成烧结试样界面脆化的重要原因之一。真空热处理能去除界面孔隙中的氢以及钨颗粒和基体相界面之中的氢,从而提高界面的结合强度,使试样的断裂强度和塑性同时得到提高。     

Fabrication of nano-crystalline W-Ni-Fe alloy with Mo and rare earth element additives

Three kinds of nano-crystalline high density alloys (86W-7Ni-3Fe-4Mo, 90W-4Ni-2Fe-4Mo and 90W4Ni-2Fe-3.8Mo-0.2RE) were fabricated by a technique combining lower temperature vacuum sintering with highenergy ball milling mechanical alloying. The crystalline size and microstructures of the specimens sintered at different sintering temperatures were examined by X-ray diffraction(XRD) and scanning electron microscope(SEM). The results show that the optimal sintering temperature of 86W-7Ni-3Fe-4Mo, 90W-4Ni-2Fe-4Mo and 90W-4Ni-2Fe-3.8Mo-0.2RE alloys are 1 300 - 1 350℃. When they are sintered at 1 300℃ for 75 min， the hardness of three kinds of specimens can reach above HRC30, the relative density can reach above 96%, and 90W-4Ni-2Fe-3.8Mo-0.2RE alloy possesses the best integrated properties, its hardness is HRC35 and its relative density is 98%.