Effect of α phase morphology on fatigue crack growth behavior of Ti−5Al−5Mo−5V−1Cr−1Fe alloy

Taking a Ti−5Al−5Mo−5V−1Cr−1Fe alloy as exemplary case, the fatigue crack growth sensitivity and fracture features with various tailored α phase morphologies were thoroughly investigated using fatigue crack growth rate (FCGR) test, optical microscopy (OM) and scanning electron microscopy (SEM). The tailored microstructures by heat treatments include the fine and coarse secondary α phase, as well as the widmanstatten and basket weave features. The sample with coarse secondary α phase exhibits better comprehensive properties of good crack propagation resistance (with long Paris regime ranging from 15 to 60 MPa·m^1/2), high yield strength (1113 MPa) and ultimate strength (1150 MPa), and good elongation (11.6%). The good crack propagation resistance can be attributed to crack deflection, long secondary crack, and tortuous crack path induced by coarse secondary α phase.     

Strain-induced α-to-β phase transformation during hot compression in Ti−5Al−5Mo−5V−1Cr−1Fe alloy

The dynamic phase transformation of Ti?5Al?5Mo?5V?1Cr?1Fe alloy during hot compression below the β transus temperature was investigated. Strain-induced α-to-β transformation is observed in the samples compressed at 0?100 K below the β transus temperature. The deformation stored energy by compression provides a significant driving force for the α-to-β phase transformation. The re-distribution of the solute elements induced by defects during deformation promotes the occurrence of dynamic transformation. Orientation dependence for the α-to-β phase transformation promotion is observed between {100}-orientated grains and {111}-orientated grains. Incomplete recovery in {111}-orientated grains would create a large amount of diffusion channels, which is in favor of the α-to-β transformation. The effects of reduction ratio and strain rate on the dynamic phase transformation were also investigated.     

Phase equilibria of Co−Mo−Zn ternary system

To experimentally determine the isothermal sections of Co−Mo−Zn ternary system at 600 and 450 °C, the equilibrated alloy and diffusion couple methods were adopted by using scanning electron microscopy coupled with energy-dispersive spectrometry, X-ray diffractometry and electron probe microanalysis. Experimental results show that there are six three-phase regions on the Co−Mo−Zn isothermal section at 600 °C and nine three-phase regions on the Co−Mo−Zn isothermal section at 450 °C. No ternary compound is found in these two isothermal sections. Both the maximum solubilities of Mo in the Co−Zn compounds (γ-Co₅Zn₂₁, γ₁-CoZn₇, γ₂-CoZn₁₃ and β₁-CoZn) and that of Zn in ε-Co₃Mo are no more than 1.5 at.%. The maximum solubilities of Zn in μ-Co₇Mo₆ are determined to be 2.1 at.% and 2.7 at.% at 600 and 450 °C, respectively. In addition, the maximum solubilities of Co in MoZn₇ and MoZn₂₂ are 0.5 at.% and 4.7 at.% at 450 °C, respectively.     

Beta Phase Parameters in the System Ti−V−Mo

As expected from similar crystal structures and favorable atomic size factors, titanium, vanadium, and molybdenum are completely soluble in one another above the transformation temperature of titanium. The β phase parameters of the continuous solid solution are shown graphically. Limiting compositions for retained β phase have been determined.     

Solubility of β-stabilizers in α-titanium

Conclusions We have determined the solubilities of iron, chromium, manganese, silicon, copper, molybdenum, vanadium, and tantalum in -titanium (Table 1) and in the -solid solution of Ti+6% Al (Table 2).Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 13–16, February, 1963     

Indentation toughness of Mo5Si3—based alloys

1　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｄｅｍａｎｄｓｆｏｒｈｉｇｈｅｒｅｆｆｉｃｉｅｎｃｙｏｆｅｎｅｒｇｙｃｏｎ ｖｅｒｔｉｎｇｓｙｓｔｅｍｓｎｅｃｅｓｓｉｔａｔｅｓｆｏｒｔｈｅｍａｘｉｍｕｍｏｐｅｒａｔ ｉｎｇｔｅｍｐｅｒａｔｕｒｅｔｏｂｅｉｎｃｒｅａｓｅｄ .     

Electromigration of H vacancies in YH3−δ

Electromigration of H vacancies in YH_3−δ is studied with the use of a simple optical technique. We analyze our results solving a linearized partial differential equation describing the process. Good agreement between experimental curves and analytical solutions is found. Our results imply that electromigration of H in this switchable mirror is dominated by a large wind force-like term.     

Solubility of sulfur in pure Cr2O3 at 1000°C

Sulfur solubility in pure Cr₂O₃ was measured over a large range of oxygen (10^–6–10^–12 atm) and sulfur (10^–2 -10^–16 atm) partial pressures at 1273 K. Different methods of analysis were used; it was found that the neutronactivation technique produced the most reliable and reproducible results. The results obtained showed that the limiting solubility of sulfur in Cr₂O₃ varied between 16–93 ppm for the range of oxygen and sulfur pressures used in this study. The solubility was found to vary, depending on the combined effect of and . For a given , the amount dissolved increases with an increase of . An empirical equation, was found to best fit the experimental results and indicates a stronger influence of than of . A specific dissolution mechanism connot be formulated from this equation. However, a number of possibilities have been proposed, but none of these specific mechanisms seems to fit the experimental data.     

Mechanical and wear properties of Mo5Si3–Mo3Si–Al2O3 composites

Mo₅Si₃ and Mo₅Si₃–Mo₃Si–Al₂O₃ composite were synthesized use MoO₃, Mo, Si and Al as raw materials by mechanically induced self propagating reaction and then consolidated by hot-pressing. The microstructure of the materials was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) with X-ray energy dispersive spectroscopy (EDS). The effects of the Al₂O₃ on the mechanical and tribological properties of Mo₅Si₃–Mo₃Si–Al₂O₃ composite have been studied. It was found that benefits associated with the addition of the Al₂O₃ to Mo₅Si₃ and Mo₃Si include finer microstructure, higher strength, higher fracture toughness and higher hardness. The dry sliding wear properties of the composite were investigated using against GCr15 bearing steel in ball-on-disk system at room temperature. The results indicated that the friction coefficients and specific wear rates of Mo₅Si₃–Mo₃Si–Al₂O₃ composite were significantly reduced by the addition of Al₂O₃, and its specific wear rates decreased by an order of magnitude compare with the monophase Mo₅Si₃. The friction coefficients of test materials decrease with an increasing load. The dominant wear mechanism of the composites was interpreted by several different wear models involving plastic deformation, adhesion, brittle fracture and reaction to form a tribo-oxidation layer.     

Cold resistance of low-carbon Mn−Ni−Mo−V steels for pressure vessels

Conclusions  

Effects of the colony size on the fracture toughness of TiAl−Mo−B alloys

The effect of the colony size on the fracture toughness of Ti−46.5Al−1.5Mo−xB (x=0.1, 0.6, 1.0) alloys was investigated. The colony size was varied by a heat treatment in the alpha-single phase region and by directional solidification (DS). The colony size decreased as the boron content increased. Fracture toughness was measured at room temperature by a three-point bend test. The heat-treated Ti−46.5Al−1.5Mo−0.1B alloy, which had a colony size of ∼350 μm, showed the best fracture toughness, and the fracture toughness decreased rapidly as the boron content increased. The fracture toughness of the DS ingots was similar with different compositions and was lower than that for the heart-treated Ti−46.5Al−1.5Mo−0.1B alloy. This study confirms that the colony size plays a major role in determining the fracture toughness of TiAl alloys with a lamellar microstructure.     

Correlation between microstructure and properties of fine grained Mo–Mo3Si–Mo5SiB2 alloys

Three phase α-Mo–Mo₃Si–Mo₅SiB₂ alloys of various compositions, namely Mo–6Si–5B, Mo–9Si–8B, Mo–10Si–10B and Mo–13Si–12B (at.%) were processed by a powder metallurgical (PM) route. Increasing the Si and B concentration in these Mo–Si–B alloys resulted in increasing volume fractions of the intermetallic phases Mo₃Si (A15) and Mo₅SiB₂ (T2) and the distribution of the three phases present in these alloys was dependent on the volume fractions of the individual phases. Above volume fractions of about fifty percent, bcc Mo solid solution (α-Mo) formed the matrix. Consequently, Mo–6Si–5B and Mo–9Si–8B alloys, which possessed a continuous α-Mo matrix provided increased fracture toughness at ambient temperatures. Additionally, a decreased BDTT of about 950 °C is caused by the homogeneous α-Mo matrix. In contrast, Mo–13Si–12B with 65 vol.% of the intermetallic phases that formed the matrix phase in this material had a BDTT value higher than 1100 °C, while the strength at elevated temperatures up to 1300 °C was significantly increased compared to alloys that have the α-Mo matrix. Alloy compositions with ≥50 vol.% of intermetallic phases (corresponding to alloys containing a minimum of 9 at.% Si and 8 at.% B) were oxidation resistant with minimal mass loss under cyclic conditions for 150 h at 1100 °C due to the formation of a dense borosilicate glass layer that protects the material surface.     

Evaluation of residual stress and corrosion behaviour of electroless plated Ni−P/Ni−Mo−P coatings

Single Ni?P and Ni?Mo?P coatings as well as duplex Ni?P/Ni?Mo?P coatings with the same compositions were prepared by electroless plating. The residual stresses of the coatings on the surface and cross sections were measured by nanoindentation and AFM analysis, and the corrosion behaviour of the coatings in 10% HCl solution was evaluated by electrochemical methods, to establish the correlation between the residual stresses and corrosion behaviour of the coatings. The results showed that the single Ni?P and duplex Ni?P/Ni?Mo?P coatings presented residual compressive stresses of 241 and 206 MPa respectively, while the single Ni?Mo?P coating exhibited a residual tensile stress of 257 MPa. The residual compressive stress impeded the growth of the pre-existing porosity in the coatings, protecting the integrity of the coating. The duplex Ni?P/Ni?Mo?P coatings had better corrosion resistance than their respective single coating. In addition, the stress states affect the corrosive form of coatings.     

Structural and mechanical properties of corundum and cubic (AlxCr1−x)2+yO3−y coatings grown by reactive cathodic arc evaporation in as-deposited and annealed states

Coatings of (Al_xCr_1?x)_2+yO_3?y with 0.51 ? x ? 0.84 and 0.1 ? y ? 0.5 were deposited on hard cemented carbide substrates in an industrial cathodic arc evaporation system from powder-metallurgy-prepared Cr/Al targets in pure O₂ and O₂ + N₂ atmospheres. The substrate temperature and bias in all the deposition runs were 575 °C and ?120 V, respectively. The composition of the coatings measured by energy dispersive X-ray spectroscopy and elastic recoil detection analysis differed from that of the facing targets by up to 11%. Microstructure analyses performed by symmetrical X-ray diffraction and transmission electron microscopy showed that corundum, cubic or mixed-phase coatings formed, depending on the Cr/Al ratio of the coatings and O₂ flow per active target during deposition. The corundum phase was promoted by high Cr content and high O₂ flow per target, while the cubic phase was observed mostly for high Al content and low O₂ flow per active target. In-situ annealing of the cubic coatings resulted in phase transformation from cubic to corundum, completed in the temperature range of 900–1100 °C, while corundum coatings retained their structure in the same range of annealing temperatures. Nanoindentation hardness of the coatings with Cr/Al ratio <0.4 was 26–28 GPa, regardless of the structure. Increasing the Cr content of the coatings resulted in increased hardness of 28–30 GPa for corundum coatings. Wear resistance testing in a turning operation showed that coatings of Al–Cr–O have improved resistance to crater wear at the cost of flank wear compared with TiAlN coatings.