Effect of tungsten particle shape on dynamic deformation and fracture behavior of tungsten heavy alloys

The effect of the tungsten particle shape on the dynamic deformation and fracture behavior of tungsten heavy alloys was investigated. Dynamic torsional tests were conducted using a torsional Kolsky bar for five alloys, one of which was fabricated by the double-cycled sintering process, and then the test data were compared via microstructures, mechanical properties, adiabatic shear banding, and fracture mode. The dynamic torsional test results indicated that in the double-sintered tungsten alloy whose tungsten particles were very coarse and irregularly shaped, cleavage fracture occurred in the central area of the gage section with little shear deformation, whereas shear deformation was concentrated in the central area of the gage section in the other alloys. The deformation and fracture behavior of the double-sintered alloy correlated well with the observation of the impacted penetrator specimen and the in situ fracture test results, i.e., microcrack initiation at coarse tungsten particles and cleavage crack propagation through tungsten particles. These findings suggested that the cleavage fracture mode would be beneficial for the self-sharpening effect, and, thus, the improvement of the penetration performance of the double-sintered tungsten heavy alloy would be expected.     

Effect of tungsten particle shape on dynamic deformation and fracture behavior of tungsten heavy alloys

The effect of the tungsten particle shape on the dynamic deformation and fracture behavior of tungsten heavy alloys was investigated. Dynamic torsional tests were conducted using a torsional Kolsky bar for five alloys, one of which was fabricated by the double-cycled sintering process, and then the test data were compared via microstructures, mechanical properties, adiabatic shear banding, and fracture mode. The dynamic torsional test results indicated that in the double-sintered tungsten alloy whose tungsten particles were very coarse and irregularly shaped, cleavage fracture occurred in the central area of the gage section with little shear deformation, whereas shear deformation was concentrated in the central area of the gage section in the other alloys. The deformation and fracture behavior of the double-sintered alloy correlated well with the observation of the impacted penetrator specimen and the in situ fracture test results, i.e., microcrack initiation at coarse tungsten particles and cleavage crack propagation through tungsten particles. These findings suggested that the cleavage fracture mode would be beneficial for the self-sharpening effect, and, thus, the improvement of the penetration performance of the double-sintered tungsten heavy alloy would be expected.     

Effect of plastic deformation on the physicomechanical properties of tungsten carbide-cobalt hard alloys

Summary A study was made of the effect of prior plastic deformation on the hardness, strength, coercive force, and electrical resistivity of tungsten carbide-cobalt hard alloys containing 10–25% cobalt. Plastic deformation decreases the hardness of the alloys. Up to a deformation of about 5–6%, all the alloys investigated showed a marked drop in hardness. Further deformation did not decrease the hardness of alloy VK25; for the alloys with lower cobalt contents, the hardness decrease was less pronounced.     

Effect of surface carburization on dynamic deformation and fracture of tungsten heavy alloys

Effects of surface carburization on dynamic deformation and fracture behavior of tungsten heavy alloys were investigated in order to improve the penetration performance. Dynamic torsional tests using a torsional Kolsky bar were conducted on four specimens, three of which were carburized by the case carburization process. The test data were then compared with hardness, Charpy impact energy, adiabatic shear banding, deformation and fracture mode, and penetration performance. With increasing carburization temperature and time, surface hardness increased, but impact energy decreased. The dynamic torsional test results indicated that for the carburized tungsten specimens, cleavage fracture occurred in the center of the gage section with little shear deformation, whereas shear deformation was concentrated at the center of the gage section for the conventionally processed specimen without carburization. The deformation and fracture behavior of the carburized specimens correlated well with the observation of the impacted penetrator specimens, i.e., microcrack initiation at tungsten particles and cleavage crack propagation. Since the cleavage fracture mode is thought to be beneficial for self-sharpening, these findings suggest the beneficial effect of the surface carburization on the penetration performance.     

Effect of initial grain size of austenite on hot-deformed structure of Ni-30Fe alloy

The microstructural evolutions of Ni-30Fe alloys during hot deformation are investigated. Hot-deformed structures of Ni-30Fe alloys with initial austenite grain sizes of 20 and 140 μm are examined under various compressive strains and deformation temperatures. As the initial austenite grain size decreases, dynamic recrystallization (DRX) occurs at lower compressive strain and lower deformation temperature. At deformation temperatures where dynamic recovery occurs instead of the DRX, hot-deformed structures consist of recovered elongated grains until fine-equiaxed grains are evolved by geometric DRX. Critical compressive strain for the geometric DRX decreases with the decrease of initial austenite grain size. Geometric DRX is evolved by the impingement of serrated grain boundaries. The decrease of initial grain size is considered to reduce the critical compressive strain needed for the impingement of serrated grain boundaries. The changes in the effective thickness of austenite grain according to the compressive deformation are examined and the effects of the restoration processes on the effective thickness of austenite grain are discussed.     

Crystallization of the amorphous alloys Fe50Ni30B20and Fe80oB20

Metallurgical and Materials Transactions A - The structure and growth characteristics of crystals growing in the amorphous alloys Fe50Ni30B20 and Fe8oB20 were studied by transmission electron...     

Redistribution of interstitial impurities in the structure of low-alloy powder metallurgy tungsten alloys in deformation

Translated from Poroshkovaya Metallurgiya, No. 12, pp. 65–69, December, 1990.     

氧含量对Ni-30Cr-1Cu镍基合金热加工性能的影响

采用小锭试验研究了氧含量对Ni-30Cr-1Cu镍基合金热加工性能的影响以及Cu在合金相中的分布.结果表明,氧含量为0.007 7%和0.015 8%的试验合金,其热加工性能显著恶化,在1 050℃和1 200℃加热后,变形量小于10%时,即在晶界普遍萌生裂纹,并沿晶界迅速扩展.氧含量为0.003 3%的试验合金,在1 050℃和1 200℃的加热温度和900℃左右的终锻条件下,均具有良好的热加工性能,一火变形量高达80%以上,仍未出现热加工缺陷.Cu只明显富集于热加工完毕空冷过程中在晶内晶界析出的M23C6中,未观察到其对热加工性能有明显的恶化作用.在正常工业生产中,采取措施把该合金氧含量控制在较低的范围内,解决了该合金热加工成形问题,取得了良好效果.     

Effect of size and shape of tungsten particles on dynamic torsional properties in tungsten heavy alloys

The effect of the size and shape of tungsten particles on dynamic torsional properties in tungsten heavy alloys was investigated. Dynamic torsional tests were conducted on seven tungsten alloy specimens, four of which were fabricated by repeated sintering, using a torsional Kolsky bar, and then the test results were compared via microstructure, mechanical properties, adiabatic shear banding, and deformation and fracture mode. The size of tungsten particles and their hardness were increased as sintering temperature and time were increased, thereby deteriorating fracture toughness. The dynamic torsional test results indicated that in the specimens whose tungsten particles were coarse and irregularly shaped, cleavage fracture occurred predominantly with little shear deformation, whereas shear deformation was concentrated into the center of the gage section in the conventionally fabricated specimens. The deformation and fracture behavior of the specimens having coarse tungsten particles correlated well with the observation of the in situ fracture test results, i.e., cleavage crack initiation and propagation. These findings suggested that there would be an appropriate tungsten particle size because the cleavage fracture mode would be beneficial for the “self-sharpening” of the tungsten heavy alloys.     

Effect of cyclic deformation on the pseudoelasticity characteristics of Ti-Ni alloys

Change in the pseudoelasticity characteristics of Ti-Ni alloys during tension cycling was investigated. The critical stress for inducing martensites and the hysteresis of a stress-strain curve decreased with increasing number of cyclic loading, while the permanent elongation increased. The degree of the change in these values showed a strong dependence on the maximum applied stress during stress-induced martensitic transformation. However, no change was induced by cyclic elastic deformation even though high stress was applied. It was also found that the stabilization of the pseudoelasticity characteristics during cyclic loading was established using special thermomechanical treatments which are effective to raise the critical stress for slip. Based on these results it is concluded that the cause for the effect of cyclic deformation is the generation of dislocations in the martensitic phase.     

放电等离子烧结制备W-9.8Ni-4.2Fe合金的高温压缩性能

采用放电等离子烧结法,通过高温压缩性能测试和扫描电镜(SEM)观察,研究粉末制备工艺和烧结温度对W-9.8Ni-4.2Fe合金在800℃下高温压缩性能的影响。结果表明,高能球磨粉末烧结合金的硬度和高温压缩性能均优于混合粉末烧结合金;在1 150℃下球磨粉末烧结合金的压缩强度最高,达到1 150 MPa,但当烧结温度在1 050~1 250℃范围内变化时,烧结合金的压缩应力应变曲线变化并不显著。     

Effect of Fe on the superplastic deformation of Zn-22 pct Al

In this investigation, the creep behavior of three grades of the superplastic Zn-22 pct Al eutectoid was studied under identical conditions of grain size, temperature, and stress. These three grades were prepared from high-purity Al and Zn using the same procedure, but they have different Fe levels: grades A, B, and C contain 423, 120, and 40 ppm of Fe, respectively. The experimental results show that the creep behavior of the three grades exhibits a sigmoidal relationship between stress and strain rate, which is manifested by the presence of three regions: region I (low-stress region), region II (intermediate-stress region), and region III (high-stress region). In region II, the creep characteristics, including the stress exponent, n, and the activation energy for superplastic flow,Q, are insensitive to Fe level; n ≅ 2.5 andQ =Q _gb, whereQ _gb is the activation energy for grain boundary diffusion. By contrast, the emergence of region I along with its stress exponent and activation energy is affected by Fe level; the higher the Fe level, the higher the stress exponent and the activation energy. The effect of Fe on region I behavior in Zn-22 pct Al is attributed to a threshold stress for creep, τ₀, whose origin is related to Fe segregation at boundaries. An examination of the estimated values of threshold stresses in the three grades along with a comparison between these values and those reported earlier for two grades of Zn-22 pct Al containing 180 ppm and 100 ppm of impurities (120 and 50 ppm of Fe, respectively) reveals two findings. First, the threshold stress appears to approach a limiting value for Fe concentrations above 120 ppm with increasing Fe level. Second, for approximately the same Fe concentration, the presence of other impurities in Zn-22 pct Al leads to a higher value of τ₀. These findings are discussed in terms of characteristics associated with grain boundary segregation (saturation and synergistic effects). Formerly Graduate Research Assistant, Materials Section, Department of Mechanical and Aerospace Engineering, University of California Formerly Research Associate, Materials Section, Department of Mechanical and Aerospace Engineering, University of California     

Effect of cobalt addition on microstructure and mechanical properties of tungsten heavy alloys

The present investigation attempts to study the microstructure and mechanical behaviour of tungsten heavy alloys with different cobalt content. Alloys with 2 and 3% cobalt were synthesized using liquid phase sintering technique. The alloys were then vacuum heat treated and finally swaged. Quantitative microstructural analyses were undertaken by determining tungsten grain size, contiguity of tungsten and volume fraction of the matrix etc. Tensile results showed that the alloy with 3% cobalt exhibited inferior properties as compared to 2% cobalt alloy. Detailed microstructural and fractographic analysis were undertaken in order to understand these trends. Work hardening analysis showed the double slope behaviour of the alloys, which could be attributed to change in deformation behaviour from single phase matrix to two phase aggregate. It was also concluded that higher cobalt alloys needed further optimization in terms of thermo-mechanical treatment in order to realize their full potential in terms of mechanical properties.     

Effect of cerium content on the deformation behavior of rapidly solidified Al-Fe-Ce alloys

The deformation behavior of a rapidly solidified Al-8.9Fe-6.9Ce (wt pct) alloy was studied in the temperature range of 250 °C to 350 °C and stress range of 20 to 175 MPa. The stress exponents and activation energies suggest that the alloy exhibits a pronounced diffusional creep regime with a transition to power law creep behavior at stresses beyond 60 MPa. Comparing these data with those obtained earlier for an Al-8.8Fe-3.7Ce alloy, it was found that in the diffusional creep regime, the Ce content had no effect on the creep rate. However, in the power law creep regime, a strong dependence on the precipitate spacing, as predicted by the structureinvariant creep law,^[5] was observed. The higher volume fraction of precipitates in the Al-8.9Fe6.9Ce alloy causes a decrease in the power law creep rates by a factor of 5. Formerly Graduate Student. Formerly Assistant Professor, University of Illinois at Urbana-Champaign.     

Effect of strain rate on the flow stress of three liquid phase sintered tungsten alloys

Stress/strain tests were carried out in compression on three liquid phase sintered tungsten alloys, with tungsten contents of 90, 95, and 97.4 wt pct, in the strain rate range 10⁻³ s⁻¹ to 10³ s⁻¹. Each alloy shows a gradual increase of flow stress with strain rate, and evidence of work softening is observed when the strain rate is of the order of 2 s⁻¹ or greater. The work softening effect is shown to result from a temperature rise due to the plastic deformation and partly masks the strain rate effect at strains greater than 0.1. The 97.4 pct tungsten alloy also shows variable behavior due to cracking associated with the presence of a brittle phase at the tungsten particle/matrix interface.