【作者】 罗述东；

【导师】 易健宏；

【作者基本信息】 中南大学 ， 材料学， 2003， 硕士

【摘要】 采用液相烧结技术，对高密度钨合金90W-7Ni-3Fe及其添加有不同含量元素Ta合金的力学性能和显微组织进行了研究。结果表明：经1480℃×1h工艺制备的90W-7Ni-3Fe合金在致密度为99.88％情况下，采取三点抗弯法测得的弹性模量E为286GPa，拉伸强度853MPa，延伸率9％，洛氏硬度HRC25.3。弹性模量随孔隙度P的增加降低迅速。经过1100℃、1200℃热处理之后虽强度略有提高、延伸率、硬度显著增加，但弹性模量却无明显变化。所得样品组织均匀，晶粒度为30μm，存在以W晶粒的穿晶断裂为主的四种断裂方式。 在添加1—7％Ta范围内合金相结构无剧烈变化，弹性模量大致随合金元素含量的升高而缓慢降低。合金强度与Ta含量关系曲线中存在一临界点成分，即5％Ta，其拉伸强度可达116MPa，在5％Ta之前随合金元素含量升高而升高，之后却快速降低。Ta的添加阻碍合金的致密化，在1440℃烧结后，所有合金密度在96—98.5％之间。合金延伸率明显恶化，除7％Ta添加合金外，其余均低于6％。85W-5Ta-TNi-3Fe合金在1100℃、1200℃热处理之后弹性模量无大的变化，但是强度却有所增加，延伸率经1100℃处理后的几乎不变，但在1200℃却降为4％。所有添加Ta样品硬度HRC均有增加，85W-5Ta-7Ni-3Fe合金达到了35.0。因Ta固溶于基体相中，降低W在基体相中的固溶度，减小了其动态速率常数，从而导致合金W晶粒细化，程度随Ta添加量增加而增强。合金的断裂模式构成发生变化，为以W晶粒穿晶断裂与基体相的延性断裂为主的方式。 高含量添加Ta(＞10％)后，粉体成形性得到改善，即弹性后效降低，压坯密度提高。因合金组织中新增Ta相，并且其含量相当高，从而弹性模量呈现与少量Ta添加时相反的结果，即弹性模量随Ta添加量增加而迅速升高，由10％Ta样品的210GPa增至40％Ta的286GPa。同时，因Ta相的出现，合金强度也表现出降低的规律。所有样品均含一定量的孔隙，延伸率也不大于3％，但硬度却随Ta含量增加而快速升高。在添加Ta量低于20％时，W晶粒尺寸仍降低，但当Ta加至30％以上时，硬质相W及Ta晶粒形状出现显著变化，不再呈现球状形态。10％Ta合金断口形貌中基体相的延性断裂和W晶粒的穿晶断裂仍是该成分合金断裂的重要形式，大量的细小W颗粒从基体相脱出，这些形式的断裂方式决定合金强度较低。Ta粉末粒度对80W-10Ta-7Ni-3Fe合金烧结致密、强度、延伸率、弹性模量、进而组织形态等性能特征都具有影响。更多还原

【Abstract】 By means of Liquid Phase Sintering (LPS), mechanical quality and micro-structure of tungsten high density alloys W-Ni-Fe and those alloys added with alloying element tantalum of different contents are investigated. The results show that under the condition of density 99.88% specimen fabricated by vacuum sintering 1480 ℃ X lh, elastic modulus of 90W-7Ni-3Fe is 286GPa through Three-Points Bending Method, strength 853Mpa, elongation 9% and hardness HRC 25.3. Elastic modulus decreases sharply with the increase of porosity. After 1100℃ and 1200℃ heating treatment, strength increases slowly and elongation, hardness are enhanced evidently, but elastic modulus has no apparent change. Sample microstructure is uniform and grain size is about 30 u m and four kinds of rupture exist in dominance of tungsten cleavage.In the range of 1-7% tantalum addition, alloys have no tremendous change in microstructure, thus elastic modulus approximately decreases as more alloying element is added. Critical point exists in the plot of strength-Ta content, namely 5%Ta, the tensile strength is as high as 1164 MPa, theretofore it increases as more Ta content is doped, but decreases subsequently. Ta blocks alloys densification, and density is in the range of 96-98.5% when sintered at 1440℃. Plasticity deteriorates and all the values are lower than 6% except specimen with 7%Ta adding. Elastic modulus of 85W-5Ta-7Ni-3Fe alloy changes scarcely after 1100℃ and 1200℃ heating treatment, but strength increases appreciably. Elongation almost has no change when treated at 1100℃, yet decreases to 4% at: 1200℃. All adulterated alloys are much harder than original W-Ni-Fe alloy, that of 85W-5Ta-7Ni-3Fe is up to HRC35.0. The solution degree of tungsten in y phase decreases because of Ta solution in matrix, therefore the kinetic rate constant is depressed, W grain size is attenuated and the degree is more obvious with the increase of Ta addition. Alloy’s fracture mode changes with the prominence of tungsten cleavage and matrix intergranular rupture.Compressibility of powders is improved when more Ta is added (>10%), namely green’s spring back is declined and pressed density increased. Because in alloys with Ta a new phase Ta appears and its content is comparative with W and matrix phase elastic modulus differs from that of alloys with lower Ta adoption. Elastic modulus increases markedly when more Ta is added, i.e. elevating 286 GPa possessed by alloy with 40% Ta from 210 GPa of 10% Ta added alloy. Meanwhile thestrength is reduced completely by reason of the abundance of Ta in alloy . All specimens bear a certain degiee of pores, thus they have an elongation capability lower than 3%, and yet hardness is elevated when alloys have a larger Ta content. Tungsten grain appears finer as 10% and 20% Ta are doped to alloys, while Ta addition is up to 30%, Ta and W grain configuration change greatly and are not spherical in shape. Matrix intergranular rupture and tungsten cleavage are still important manners in the micrograph of 80W-10Ta-7Ni-3Fe alloy, and lots of fine W grain separates with matrix, which determines its bad tensile strength. Particle size possesses influence on densification, strength, elongation, elastic modulus and micrograph of 80W-10Ta-7Ni-3Fe alloy.更多还原