M. E. Golovkova

The Structure and Properties of Calcium Phosphate Ceramics Produced from Monetite and Biogenic Hydroxyapatite

It is shown that porous calcium phosphate ceramics can be produced from monetite and biogenic hydroxyapatite, the starting materials being in the ratios 25 : 75, 50 : 50, and 75 : 25 wt.%. It is established that phase transitions and solid-phase reactions take place during sintering to form polyphosphate ceramics consisting of hydroxyapatite (Ca5(PO4)3(OH)), β-pyrophosphate (β-Ca2P2O7), and β-tricalcium phosphate (β-Ca3(PO4)2), in which β-Ca2P2O7 and Ca5(PO4)3(OH) phases are predominant, depending on starting composition. When the biogenic hydroxyapatite content changes from 25 to 75 wt.%, the grain size decreases and the pore size increases. The ceramics have 40 to 42% porosity with predominant open porosity for all compositions. The ceramics show 32–55 MPa strength, which increases with the amount of biogenic hydroxyapatite in starting composition.

Interaction of Molybdenum with Cobalt–TiN and Cobalt–Copper Melts

The solubility of molybdenum in Co–Cu and Co–Sn melts and the growth of Mo6Co7layer at the molybdenum–melt interface at 1200°C are examined. The solubility of molybdenum in these melts is well described by the equations: lgCMo= −3.642 + 24.589 ⋅ CCo– 134.787 ⋅ CCo2(Co–Cu melt) and lgCMo= −3.363 + 6.552 ⋅ CCo– 6.284 ⋅ CCo2(Co–Sn melt). The melt composition (in atomic fractions) in the three-phase Mo–Mo6Co7–melt equilibrium is established: CCo= 5.34 ⋅ 10−3, CMo= = 3.05 ⋅ 10−4, the rest being Cu (Co–Cu melt); CCo= 0.176, CMo= 5.7 ⋅ 10−3, the rest being Sn (Co–Sn melt). The substantial difference in growth rate constants in the melts (kCo–Sn>> kCo–Cu) with the same cobalt activity αCois attributed to the impact of admixtures (Cu and Sn) on the growth of the Mo6Co7layer. Data on the solubility of molybdenum in Co–Cu and Co–Sn melts and the growth kinetics of Mo6Co7are obtained for the first time.

Effect of Process Conditions on the Structure and Properties of the Hot-Forged Fe3Al Intermetallic Alloy

Two kinds of powder mixtures are used for producing Fe3Al intermetallic alloys. The mixtures are prepared by mixing elemental powders in a drum mixer or grinding in a planetary mill. Compacted and sintered from this mixtures, the billets are subjected to the hot forging and annealing at 1100 and 1300°C. The effect of process conditions on the structure and properties of the materials produced is investigated. It is established that, after hot forging, the strength and fracture toughness of the intermetallic alloy produced from a ground charge are higher than those of the intermetallic alloy produced from non-ground charge. The annealing of the samples at 1100°C causes the decrease in the strength and fracture toughness of both alloys, while increasing the annealing temperature to 1300°C leads to some increase in these characteristics. The hardness of the intermetallic alloy prepared from non-ground powders is higher in comparison with that prepared from pre-ground charge and the annealing and its temperature increase lead to a noticeable decrease in the material hardness.

Structure and Properties of Sintered Silicon–Manganese Steels

The effect of the content of manganese silicide (MnSi1.77) additive in the original charge and sintering temperature on the structure and properties of sintered steels is investigated. It is shown that adding manganese silicide slightly decreases the density of sintered samples, but significantly increases the hardness and strength properties of the alloys. An electron microprobe analysis of sintered steels establishes that manganese is relatively uniformly distributed in iron particles, whereas the distribution of silicon is significantly different: its higher concentration is mainly seen along the grain boundaries.

High fracture toughness of powder chromium sintered in magnesium vapor

The fracture toughness of powder chromium sintered in magnesium vapor is higher by a factor of 53 than that of powder chromium sintered in hydrogen and by a factor of 5 than that of deformed low-alloy chromium VKh2K castings. This high fracture toughness is due to the skeleton formed of plastic interlayers of high-purity chromium. Chromium becomes highly ductile after fine purification in Cr–MgO alloys to remove interstitial impurities. The interlayers form on the surface of chromium powder particles under the refining action of magnesium vapor. Auger electron microscopy and data on fracture, chemical composition, and etching resistance lead to the conclusion that there are interlayers made of pure chromium. The high fracture toughness remains after annealing for 1 h at 1500°C.