Trace Carbon Addition to Refine Microstructure and Enhance Properties of Additive-Manufactured Ti-6Al-4V

Carbon is a powerful alloying element for titanium alloys. In this work, trace carbon is alloyed with Ti-6Al-4V during wire?+?arc additive manufacturing, and the effects on the solidification process, microstructure and mechanical properties are explored. With between 0.03 wt.% and 0.41 wt.% carbon, the prior-β grain size and α-lath length reduce by factors of 5–6 which is attributed to separate grain refining mechanisms. Alloying Ti-6Al-4V with up to 0.1 wt.% carbon improved both the tensile strength and ductility, but higher carbon additions were associated with excessive carbide formation and severe embrittlement.     

Titanium-Lead System

The Ti-Pb diagram was investigated in the region 0 to 58 pet Pb and from 500°C to liquidus temperatures. Three reactions were encountered: 1—β→α+Ti₄Pb at 725±10°C; 2—β+L→Ti₄Pb at 1305±10°C; and 3—the possible eutectic L→Ti₄Pb and γ between 1200° and 1300°C.     

Beta-Omega Age Hardening Means Stronger Zirconium Alloys

The β-ω phase transformation, important in many titanium alloys, has been revealed in zirconium alloys. Hitherto unattainable tensile strength with adequate ductility is now feasible for certain zirconium alloys. It is expected that many new applications will result from this discovery.     

Transformation kinetics and mechanical properties of Zr-Mo alloys

Alloys containing 1.3, 3.3, 5.4, and 7.5 pct Mo were prepared using high purity molybdenum and sponge zirconium. Time-temperature-transformation curves were established for these alloys based on the resistivity vs time of anneal curves of isothermally quenched rods. Tensile and impact bars of each alloy were heat treated by isothermal quench techniques as well as by quench and reheat treatments. These bars were then machined, tested, and the properties compared. Optimum properties could be developed in the 1.3 pct Mo alloy using the isothermal quench technique. The 3.3, 5.4, and 7.5 pct Mo alloys exhibited a brittle behavior irrespective of type of heat treatment. An ω or transition phase in the β → α transformation was discovered which undoubtedly accounts for most of the brittleness observed. The ω phase has been tentatively indexed as tetragonal, c/a= 1.45. Mechanical properties of unalloyed sponge zirconium are presented for comparison.     

Effect of nitrogen on sigma formation in Cr-Ni steels at 1200°F (650°C)

The addition of nitrogen (0.10 to 0.20 pct) to Fe-Cr-Ni alloys of simulated commercial purity results in a real displacement of the σ phase boundaries to higher chromium contents. The effect is small for the (γ + σ)/γ boundary, but is pronounced for the (γ + α + σ)/(γ + α) boundary. Although there is an indication of an exceptionally large shift of the σ boundaries to higher chromium contents, especially in steels with nitrogen over 0.2 pct, the major portion of this apparent shift results from the fact that carbide and nitride precipitation cause “chromium impoverishment” of the matrices. The effect of combined additions of nitrogen and silicon to the Fe-Cr-Ni phase diagram is demonstrated also. Nitrogen can nullify the effect of about 1 pct Si in shifting the (γ + σ)/γ phase boundary to lower values of chromium at all nickel levels from 8 to 20 pct. Nitrogen can nullify this σ-forming effect of about 2 pct Si at the 8 pct Ni level, but not at the 20 pct Ni level. The alloys studied were in both the cast and the wrought conditions. There are indications that the σ phase forms more slowly in the cast alloys than in the wrought alloys if both are in the completely austenitic state. The presence of δ ferrite in the cast alloys accelerates the formation of σ. Cold working increases the rate of σ formation in both cast and wrought alloys.     

Structure and Thermoelastic Martensitic Transformations in Ternary Ni–Ti–Zr Alloys with High-Temperature Shape Memory Effects

X-ray diffraction analysis and transmission electron and scanning electron microscopies were used to study the effect of alloying with zirconium (0–20 at %) on the phase composition and structural and morphological features of thermoelastic martensitic transformations in ternary Ni–Ti–Zr alloys. The electrical resistivity of alloys has been measured in a wide range of temperatures, the critical temperatures have been determined, and a complete diagram of the high-temperature thermoelastic forward and reverse martensitic transformations B2 ? B19' occurring with a hysteresis in the range of 32–50 K has been constructed based on XRD data. The intercritical range of the temperatures of transformations increases as the zirconium content increases within the indicated limits. The lattice parameters of the monoclinic crystal lattice of the B19' martensite have been measured at room temperature. The twinning types most frequently observed in B19' martensite have been found as follows: I-(011), \(\left( {11\;\bar 1} \right)\) and (001), II-(011).     

Hydrogen Embrittlement of Beta-Stabilized Titanium Alloys

The α-β type alloys are subject to a loss of tensile ductility with increasing hydrogen content. No hydride phase is visible in embrittled α-β type alloys. The embrittlement encountered appeared to be of the strain-aging type. Both compositional and structural factors are shown to influence the hydrogen tolerance of α-β type alloys.     

Phase Equilibria and Microhardness of As-Cast and Annealed Ni-Al-Os Alloys in Ni-Rich Region

In this paper, the isothermal section at 1273 K and liquidus projection of ternary Ni-Al-Os system in Ni-rich region were firstly measured by using 6 annealed and 6 as-cast Ni-Al-Os alloys with 65 at.% Ni in combination with x-ray diffraction, optical microscopy and electron probe microanalysis techniques. For the determined partial isothermal section at 1273 K, 2 single-phase, 4 two-phase and 2 three-phase regions were observed. The solubilities of Os in both γ and γ′ phases were also determined. For the proposed liquidus projection, four primary surfaces of γ′, γ, β and δ, and two invariant reactions were identified. Secondly, the microhardness of both as-cast and annealed alloys were measured. The evolution trend of microhardness in both as-cast and annealed alloys with Os addition generally increases first, and then decreases. Thirdly, the further comprehensive discussion on possible substitution of Re by Os in new-generation nickel-based single-crystal superalloys were performed in terms of strengthening degree, high-temperature creep resistance, and possibility for formation of harmful topologically close-packed phases. It was finally concluded that Os may be used as a new additional element to replace or partly replace Re in Ni-based single crystal superalloys.     

Structure of the transition phase omega in Ti-Cr alloys

Ti-Cr alloys age harden after β-quenching by formation of an ω-phase. The structure and orientation of this transition phase have been determined. The hardness appears to be caused by strain in the β-matrix produced by concurrent enrichment of alloy content in the ω-phase.     

High-speed anode dissolution of heat-resistant chrome-nickel alloys containing tungsten and rhenium: III. Chloride-nitrate solutions

The anodic dissolution rates of two heat-resistant tungsten (12 wt %) and tungsten and rhenium (8 wt % W : 6 wt % Re) alloys in chloride, nitrate, and chloride-nitrate (30 g/l NaCl : 120 g/l NaNO₃) electrolytes have been compared. An excess of the critical current density i _crit depending on the hydrodynamic conditions leads to (i) the decreasing dependence of the current efficiency on the current density and (ii) the independence of the dissolution rate on the solution content. The mass-transfer mechanism, which determines the dissolution rate and the structure of superficial layers at i > i _crit, is discussed. Data on the chemical content of the surface layers depending on the machining modes are presented. The modes of the electrochemical dimensional machining (ECDM) of the parts made of these alloys are offered to attain the best performance parameters for machining.     

Mechanical properties of alpha titanium as affected by structure and composition

The effects of grain size and shape on alloys of titanium with nitrogen and aluminum have been determined. Increasing α grain size decreases strength and hardness and increases impact resistance. Quenching from the β field produces subgrain markings delineating α plates in Ti-N alloys but not in Ti-Al alloys. This suggests a precipitation from the high nitrogen alloys.     

Experimental Investigation of the Binary Mn-Sb Phase Diagram

The binary manganese-antimony (Mn-Sb) phase diagram was reinvestigated in the whole composition range using powder-XRD, DTA and SEM-EDX. The phase boundaries and melting temperatures of the ferromagnetic phases MnSb and Mn₂Sb were modified by taking into account the new experimental data. Most of the reaction temperatures could be verified within a range of ±10 °C. Nevertheless, a few temperatures had to be revised, such as the eutectic reaction L → β-Mn + Mn ₂ Sb at 893 °C and the eutectoid reaction β-Mn → α-Mn + Mn ₂ Sb at 718 °C. The previously reported peritectic melting behavior of MnSb could be confirmed. The variation of the lattice parameters of the NiAs-(B8 ₁ ) type MnSb phase with composition was determined. A revised version of the of the Mn-Sb phase diagram is presented.     

Prediction of Martensite Start Temperature for Lightweight Fe-Mn-Al-C Steels

A tailor-made thermodynamic database of the Fe-Mn-Al-C system was developed using the CALPHAD approach. The database enables predicting phase equilibria and thereby assessing the resulting microstructures of Fe-Mn-Al-C alloys. Available information on the martensite start (M_s) temperature was reviewed. By employing the M_s property model in the Thermo-Calc software together with the new thermodynamic database and experimental M_s temperatures, a set of model parameters for the Fe-Mn-Al-C system in the M_s model was optimised. Employing the newly evaluated parameters, the calculated M_s temperatures of the alloys in the Fe-Mn-Al-C system were compared with the available measured M_s temperatures. Predictions of M_s temperatures were performed for the alloys, Fe-10, 15 and 20 wt.% Mn-xAl-yC. The predictability of the M_s model can be further validated when new experimental M_s temperatures of the Fe-Mn-Al-C system are available.     

Heat treatment,structure, and mechanical properties of Ti-Mn alloys

Ti-Mn alloys were studied in order to determine the factors affecting the mechanical properties of β-stabilized titanium alloys. The principal compositional factors have been found to be solid-solution strengthening, the martensitic transformation, and instability of the β phase. Structural factors, such as grain size and shape, were found to have more influence on ductility and toughness than on strength.     

Microstructure and Room-Temperature Mechanical Properties of FeCrMoVTi<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> High-Entropy Alloys

FeCrMoVTi _x (x values represent the molar ratio, where x = 0, 0.5, 1.0, 1.5, and 2.0) high-entropy alloys were prepared by a vacuum arc melting method. The effects of Ti element on the microstructure and room-temperature mechanical properties of the as-cast FeCrMoVTi _x alloys were investigated. The results show that the prepared alloys exhibited typical dendritic microstructure and the size of the microstructure became fine with increasing Ti content. The FeCrMoV alloy exhibited a single body-centered cubic structure (BCC1) and the alloys prepared with Ti element exhibited BCC1 + BCC2 mixed structure. The new BCC2 phase is considered as (Fe, Ti)-rich phase and was distributed in the dendrite region. With the increase of Ti content, the volume fraction of the BCC2 phase increased and its shape changed from a long strip to a network. For the FeCrMoV alloy, the fracture strength, plastic strain, and hardness reached as high as 2231 MPa, 28.2%, and 720 HV, respectively. The maximum hardness of 887 HV was obtained in the FeCrMoVTi alloy. However, the fracture strength, yield stress, and plastic strain of the alloys decreased continuously as Ti content increased. In the room-temperature compressive test, the alloys showed typical brittle fracture characteristics.     

The Effect of Oxygen on Phase Equilibria in the Ti-V System: Impacts on the AM Processing of Ti Alloys

Oxygen is always a constituent in “real” titanium alloys including titanium alloy powders used for powder-based additive manufacturing (AM). In addition, oxygen uptake during powder handling and printing is hard to control and, hence, it is important to understand and predict how oxygen is affecting the microstructure. Therefore, oxygen is included in the evaluation of the thermodynamic properties of the titanium-vanadium system employing the CALculation of PHAse Diagrams method and a complete model of the O-Ti-V system is presented. The β-transus temperature is calculated to increase with increasing oxygen content whereas the extension of the α-Ti phase field into the binary is calculated to decrease, which explains the low vanadium solubilities measured in some experimental works. In addition, the critical temperature of the metastable miscibility gap of the β-phase is calculated to increase to above room temperature when oxygen is added. The effects of oxygen additions on phase fractions, martensite and ω formation temperatures are discussed, along with the impacts these changes may have on AM of titanium alloys.     

Microstructure,Phase Occurrence,and Corrosion Behavior of As-Solidified and As-Annealed Al-Pd Alloys

In the present work, we studied the microstructure, phase constitution, and corrosion performance of Al₈₈Pd₁₂, Al₇₇Pd₂₃, Al₇₂Pd₂₈, and Al₆₇Pd₃₃ alloys (metal concentrations are given in at.%). The alloys were prepared by repeated arc melting of Al and Pd granules in argon atmosphere. The as-solidified samples were further annealed at 700 °C for 500 h. The microstructure and phase constitution of the as-solidified and as-annealed alloys were studied by scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray diffraction. The alloys were found to consist of (Al), ε _n (~ Al₃Pd), and δ (Al₃Pd₂) in various fractions. The corrosion testing of the alloys was performed in aqueous NaCl (0.6 M) using a standard 3-electrode cell monitored by potentiostat. The corrosion current densities and corrosion potentials were determined by Tafel extrapolation. The corrosion potentials of the alloys were found between ? 763 and ? 841 mV versus Ag/AgCl. An active alloy dissolution has been observed, and it has been found that (Al) was excavated, whereas Al in ε _n was de-alloyed. The effects of bulk chemical composition, phase occurrence and microstructure on the corrosion behavior are evaluated. The local nobilities of ε _n and δ are discussed. Finally, the conclusions about the alloy’s corrosion resistance in saline solutions are provided.     

Investigation of the heat treatment of commercial titanium-base alloys

An exploratory survey of the heat treatment response of commercial titanium alloys (Ti-150A, RC-130B, and MST 3Al-5Cr alloys) shows a wide range of possible hardness and microstructural characteristics. The hardening is primarily dependent on the solid state transformation of the βphase. An age hardening reaction which apparently is associated with β decomposition and precipitation has been shown. Brittleness and notch sensitivity appear to be characteristic of age hardening to high hardness. Ductility, tensile strengths, and elongations are given.     

Strain induced transformation in beta brass

The β-phase of Cu-Zn and Cu-Zn-Ga alloys partially transforms when cold worked at low temperatures. X-ray data are presented on the new structures formed (which depend upon composition), on densities of stacking faults in them, on M_d temperatures, and on the tendency to revert to body-centered-cubic structure.     

Improved High-Temperature Microstructural Stability and Creep Property of Novel Co-Base Single-Crystal Alloys Containing Ta and Ti

The influence of Ta and Ti additions on microstructural stability and creep behavior in novel Co-Al-W base single-crystal alloys has been investigated. Compared to the ternary alloy, the γ′ solvus temperature and γ′ volume fraction were raised by individual additions of Ta and Ti, and increased further in the quinary alloy containing both alloying additions. In contrast to ternary and quaternary alloys, an improved microstructural stability with the stable γ–γ′ two-phase microstructure and more than 60% γ′ volume fraction existed in the quinary alloy after prolonged aging treatment at 1050°C for 1000 h. The creep behavior at 900°C revealed lower creep rates and longer rupture lives in the quaternary alloys compared to the ternary alloy, whereas the quinary alloy exhibited even better creep resistance. When the creep temperature was elevated to about 1000°C, the creep resistance of the quinary alloy exceeded the previously reported Co-Al-W-base alloys and first-generation Ni-base single-crystal superalloys. The improved creep resistance at approximately 1000°C was considered to be associated with high γ′ volume fraction, γ′ directional coarsening, and dislocation substructure, which included γ–γ′ interfacial dislocation networks and the sheared γ′ precipitates containing stacking faults and anti-phase boundaries.