Matrix composition effects on the tensile properties of tungsten-molybdenum heavy alloys
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finement through incorporation of molybdenum, tantalum, or rhenium, c~-15j These additions are soluble in both the tungsten and matrix phases and retard solutionreprecipitation during liquid phase sintering. In this study, the alloy composition was varied in the nickel/iron ratio and molybdenum was partially substituted for tungsten. The sintered tensile properties were assessed v s these compositional variations. The powders for this investigation are identified in Table I. The experiments were performed with a constant Ni + Fe content (by weight) of 10pct and a constant W + Mo content of 90 pct. Two levels of the N i / F e ratio were considered, 7 / 3 and 8/2. The 7/3 ratio is most popular in the commercial alloys, while the 8/2 ratio gives slightly greater tungsten solubility in the matrix and, thereby, increases the sintered grain size and ductility. [6'16] The molybdenum content was varied in 4 pct increments from 0 to 16 pct. The constituent powders were mixed in a turbula mixer for 1 hour and die compacted into flat tensile bars at 275 MPa with zinc stearate as a die wall lubricant. Sintering was performed at a maximum temperature of 1500 ~ for 30 minutes in a hydrogen atmosphere with a varying dew point to minimize retained porosity, t3,~21 Subsequently, the tensile samples were annealed at 1100 ~ for 1 hour and water quenched. The density was determined by water immersion, and tensile properties were measured on two or three replica samples at room temperature. Table II summarizes the average results of the experiments. The property variations between specimens were typically +--0.02 g / c m 3 (density), ---20 MPa (strength), +-1.5 pct (elongation), and +-0.3 HRA (hardness). For comparison purposes, typical tensile strengths for 90 pct W-7 pct Ni-3 pct Fe alloys range up to 950 MPa with a failure elongation in the 35 to 40 pct range. I4,171
A. BOSE and R.M. GERMAN Tungsten-base heavy alloys are liquid-phase sintered from mixed tungsten, nickel, and iron powders. The sintered product is a composite consisting of interlaced tungsten and solidified matrix (W-Ni-Fe) phases. These alloys are most useful in applications requiring high density, strength, and toughness. The design of improved tungsten heavy alloys has been the subject of several research investigations as summarized in References 1 through 5. Much success has taken place through improved processing, but parallel compositional studies have resulted in new microstructure-property combinations. As part of these investigations, the N i / F e ratio has been varied, with the general conclusion that optimal strength and ductility occur with a ratio between 2 and 4. [6'71Brittle intermetallic phases can form outside of this composition range, t8] Historically, a 7/3 Ni/Fe ratio has been selected for processing studies. [9,~~ Recently, Spencer and Mullendore t~l reported higher ductilities and impact energies for 90 and 93 pct W heavy alloys with the 8/2 N i / F e ratio. Alternatively, these alloys can be strengthened by both solid solution and grain size
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