Fine Ti Research Articles

The effect of Ti–Mo–Nb on the microstructures and tensile properties of a Fe–Mn–Al–C austenitic steel

An investigation was performed to evaluate the effect of the Ti–Mo–Nb co-addition on the microstructure and the tensile behavior of a Fe–26Mn–8Al-1.5C austenitic steel after aging at temperatures from 500 to 600 °C. The co-addition of Ti–Mo–Nb in the steel refines grains, increases the sizes and volume fractions of κ-carbides, and forms inter- and intra-granular (Ti,Mo,Nb)C particles. The promotion effect of Ti–Mo–Nb on the κ-carbides precipitation varies with different aging temperature. The steel with co-addition of Ti–Mo–Nb possesses higher yield strength due to the combination of grain refinement, more κ-carbides precipitation, and the formation of fine (Ti,Mo,Nb)C particles distributed uniformly within the grains, but has lower ductility ascribed to the coarseness of κ-carbides with larger volume fraction and the existence of micron-sized inter-granular (Ti,Mo,Nb)C particles along the grain boundaries. With aging temperature increasing, the strength increases but the ductility decreases for both steels with and without microalloying. In addition, the strengthening mechanisms were analyzed quantitatively. The results show that the precipitation hardening is the dominant strengthening mechanisms for both steels.

Improved toughness of double-pass welding heat affected zone by fine Ti–Ca oxide inclusions for high-strength low-alloy steel

In order to improve the mechanical performance of double-pass welding heat affected zone, acicular ferrite (AF) induced by Ti–Ca oxide inclusions was used to enhance the toughness properties of the intercritically reheated coarse-grained heat-affected zone (ICCGHAZ). The microstructural evolution and toughness mechanisms in the coarse-grained heat-affected zone (CGHAZ) and ICCGHAZ containing different oxide inclusions were studied by thermo-mechanical simulator, optical and electron microscopy, electron back-scattered diffraction and mechanical testing. The results indicated that CGHAZ toughness was decreased and Vickers hardness was increased compared with the base metal in Ti–Ca deoxidized and Al–Ca killed steels. However, the toughness loss in Al–Ca killed steel was more significant. In Ti–Ca steel, dominant Ti–Ca–O–Mn–S oxide inclusions of size between ~0.2 and 1.6 μm effectively promoted AF transformation. After the double-pass thermal cycle, AF plates were retained and the prior martensite/bainite structure in CGHAZ transformed into fine ferrite/bainite structure. As a result, the toughness of ICCGHAZ in Ti–Ca steel was significantly enhanced from ~94 J to ~209 J. In the Al–Ca steel, dominant Al–Ca oxide inclusions were ineffective for microstructure refinement and acted as a potential crack initiation site. The formation of coarse granular bainite and lath-like martensite/austenite (M/A) constituents led to deterioration of toughness in CGHAZ (~20 J) and further loss in ICCGHAZ (~13 J).

Development of Superfine-grained Cemented Carbide (SCPT alloy) by Pinning Effect of Fine Ti(C,N) Particles

Development of Superfine-grained Cemented Carbide (SCPT alloy) by Pinning Effect of Fine Ti(C,N) Particles

Fabrication and Properties of (Ti, W, Mo, Nb, Ta)(C, N)-Co-Ni Cermets

Fine single-phase (Ti, W, Mo, Nb, Ta)(C, N) solid solution powders were synthesized through the carbothermal reduction method. (Ti, W, Mo, Nb, Ta)(C, N)-Co-Ni cermets were fabricated via vacuum sintering. Micrographs of powders and microstructures of the cermets were observed using transmission electron microscopy and scanning electron microscopy in combination with energy-dispersive spectroscopy. Phase compositions were investigated using x-ray diffraction. The C and N contents were measured using elemental analysis (CHNS/O). The optimized conditions for the synthesis process of single-phase (Ti, W, Mo, Nb, Ta)(C, N) solid solution powders with high nitrogen content were 1500 °C for 2 h under a 2 kPa nitrogen atmosphere. Under such conditions, the particle size of the synthesized powder was less than 140 nm, and its carbon and nitrogen contents were 9.174 and 7.040 wt.%, respectively. The synthesized fine (Ti, W, Mo, Nb, Ta)(C, N) solid solution powders had a significant positive impact on the strengthening and hardening of Ti(C, N)-based cermets. The values of hardness and transverse rupture strength of the (Ti, W, Mo, Nb, Ta)(C, N)-Co-Ni cermets sintered at 1450 °C for 1 h in vacuum (SSC3) increase by 14.7 and 20.2% compared to those of traditional Ti(C, N)-WC-Mo2C-NbC-TaC-Co-Ni cermet (TC), respectively. However, the KIC value of SSC3 decreases by 14.1% compared to that of TC. The mechanism of strengthening and hardening and the cause of the low fracture toughness of the SSC were revealed by comparing the differences in the microstructures of SSC and TC.

Effect of Zr Microalloying on Austenite Grain Size of Low-Carbon Steels

The effect of microalloying addition of Zr on the characteristics of inclusions and prior austenite grain sizes following a quench heat treatment has been investigated for two custom-made steels. The average size of particles in the Zr-containing steel is found to be the same as the Zr-free steel (0.49 μm). However, the number of smaller particles in the Zr-containing steel is much higher than the Zr-free steel. The inclusions in the Zr-containing steel are composed of ZrO2-TiN-MnS, and inclusions in the Zr-free steel are consisted of TiOx-Ti(C,N). The average prior austenite grain size of the Zr-containing steel is consistently smaller than that of the Zr-free steel, due to a large number of fine oxide inclusions and Ti(C,N) precipitates, working to pin the austenite grain boundaries at temperatures up to 1673 K (1400 °C). The grain refinement mechanisms by inclusions through the addition of Zr are discussed via thermodynamic and kinetic calculations.

Development of nano-structure China low-activation martensitic steel for fusion reactors

Herein, we report a new castable nanostructured alloy (CNA), which was first melted in a vacuum induction furnace to introduce micron- and submicron-sized inclusions, strengthened by the multiscale secondary phases for fusion reactors. The large micron-scale inclusions are removed, whereas submicron-scale inclusions were retained during an electroslag remelting process. The ingot was subjected to heat treatment at 1050 °C for 0.5 h followed by heating at 650 °C for 1.5 h to obtain tempered martensite along with the nanosized (Ti, W) carbides. The improvement in the mechanical properties of the sample treated at 750 °C was attributed to the removal of blocky Y-rich inclusions along with the strengthening of the submicron-sized Y2O3 oxides. The performance of the sample treated at 650 °C was explained by the precipitation of the fine (Ti, W) carbides.

The effect of V addition on microstructure and tribological properties of Fe-Ti-C claddings produced by gas tungsten arc welding

The microstructure of the cladded layers consisted of carbide particles and primary Fe3C blades in pearlite-ledeburite matrix. The addition of V into the cladded layer increased the volume percentage of carbide particles and led to the formation of relatively fine (Ti,V)C complex carbides with uniform distribution in the matrix, while the volume percentage of the primary Fe3C phase decreased. With increasing the weight percentage of V in the cladding layers, the microhardness and wear resistance of the cladding layers increased which was due to the increase in volume percentage of (Ti,V)C complex carbides and the strengthening effect of the matrix by V. The addition of V up to 5 wt.% to the two passes Fe-Ti-C cladding layer increased the hardness from 51 to 62 HRC. The wear weight loss decreased by about 60%. The predominant wear mechanisms of the cladded samples were separation of carbides and adhesive wear. In the cladded layer containing higher vanadium content, the separation of carbides decreased and lower adhesive wear was seen.

The significant impact of Ti content on microstructure–toughness relationship in the simulated coarse-grained heated-affected zone of high-strength low-alloy steels

ABSTRACTThis study aims to investigate the influence of Ti addition on microstructure and toughness in the simulated coarse-grained heated-affected zone (CGHAZ) of high-strength low-alloy steels. The steels with low and high Ti content respectively were subjected to 100 kJ/cm heat input welding thermal cycle. The results indicated that the second-phase particles were mainly oxide covered with MnS and fine (Ti,Nb)N precipitate in low-Ti steel, which were modified to the oxide surrounded by TiN and coarse (Ti,Nb)N precipitate in high-Ti steel. Compared with low-Ti steels, the coarser precipitates induced larger austenite grain in CGHAZ of high-Ti steel. Moreover, the wrapping of TiN decreases the ability of inclusion to promote the nucleation of acicular ferrite, resulting in lower fraction of acicular ferrite in CGHAZ of high-Ti steel. Content of martensite-austenite constituent increased in CGHAZ of high-Ti steel. They were all responsible for the degeneration in toughness in CGHAZ of high-Ti steel.

Phase precipitation behavior and tensile properties of as-cast Ni-based superalloy during heat treatment

Abstract The phase precipitation behavior and tensile properties of an as-cast Ni-based alloy, IN617B alloy, after solution heat treatment and long-term aging treatment were investigated. Ti(C,N), M6C and M23C6 are the primary precipitates in as-cast microstructure. After solution heat treatment, most of carbides dissolve into the matrix except a few fine Ti(C,N) within grains. During long-term aging at 700 °C, the phase precipitation behaviors of the alloy are characterized as follows: (1) M23C6 carbides at grain boundaries (GBs) transform from film-like shape to cellular shape and gradually coarsen due to the decrease of the surface energy and element aggregation to GBs; (2) M23C6 carbides within grains have a bar-like morphology with a preferential growth direction [110] and have a cube-on-cube coherent orientation relationship with the matrix γ; (3) γ′ particles inhibit the coarsening of M23C6 within grains by constraining the diffusion of formation elements. Furthermore, the tensile strength of the alloy obviously increases, but the ductility significantly decreases after the aging for 5000 h. The alloy has a relatively stable microstructure which guarantees the excellent tensile properties during long-term aging.

Microstructure and high strength–ductility synergy of Ti–6Al–4V alloy induced by joule heat treatment

The fine grain Ti–6Al–4V alloy fabricated by the multi-rolling process was annealed by a joule heat itself. The effects of subgrain development and growth on the strength and its ductility were investigated. The values of yield strength and elongation of all the specimens exceeded 860 MPa and 10% (ASTM), respectively. And excellent strength (1040 MPa, yield strength; 1104 MPa, tensile strength) and ductility (13.5%, elongation; 52%, area reduction) could be obtained resulting from the high boundary intensity and fine grain size.

Study of the Microstructure, Crystallographic Structure and Thermal Stability of Al–Ti–Nb Alloys Produced by Selective Electron Beam Alloying

This paper aims an investigation of the microstructure and crystallographic structure as well as the thermal stability of Al–Ti–Nb formed by selective electron beam surface alloying. The fabrication of the samples has been carried out using circular sweep mode, as two velocities of the sample movement have been chosen: V1 = 1 cm/s and V2 = 0.5 cm/s. The studied microstructure and crystallographic structure have been investigated by X-ray diffraction (XRD) and Scanning electron microscopy (SEM) respectively. The thermal behavior of the obtained surface alloys are evaluated by the coefficient of thermal expansion (CTE) which has been evaluated by neutron diffraction measurements at high temperature. The results show that in the earlier stages of formation, the microstructure of the intermetallic phase is mainly in the form of coarse fractions, but at the following moments they dissolve, forming separated alloyed zone and base Al substrate as the alloyed zone consists of fine (Ti,Nb)Al3 particles dispersed in the Al matrix with small amount of undissolved intermetallic fractions. Formation of preferred crystallographic orientation as a function of the speed of specimen motion has not been observed. The performed neutron diffraction measurements show that the lattice parameters of the obtained intermetallic (Ti,Nb)Al3 are less upshifted in comparison to pure Al. It has been found that the aluminium lattice is much more unstable at high temperatures than that of the intermetallic phase. The CTE for the intermetallic phase is 8.70 ppm/K for a axis and 7.75 ppm/K for c axis respectively while considering Al it is 12.95 ppm/K.

SEM and TEM analysis of composite of ZrO2-Ti system

3Y-ZrO2-Ti composites obtained by slip casting method were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Moreover, the Vickers hardness was measured. The experiments show the complex microstructure of composites. The tetragonal zirconium dioxide (t-ZrO2) and monoclinic zirconium dioxide (m-ZrO2) as a composite matrix were detected at XRD analysis. SEM observations revealed that Ti -rich phase are uniform distributed in composites. Moreover, the large and very fine precipitations were found. The very fine Ti rich precipitations were located at ZrO2 grain boundaries as well as in the triple-points. TEM experiments confirmed that in the sintered composites 3Y-ZrO2 – 10%Ti the uniaxial ZrO2 grains (100–600 nm), fine monoclinic martensitic plates and fine round monoclinic particles (20–40 nm) of ZrTiO2 phase were exist. The complex microstructures of 3Y-ZrO2-Ti composites have a high hardness as a result of existing fine ZrTiO2 and other Ti oxides precipitations.

Fine Ti‐dispersed Al2O3 composites and their mechanical and electrical properties

AbstractAl2O3/Ti composites containing 0‐30 vol% dispersed fine Ti particles were fabricated using a hot‐press sintering method at 1500°C from mixtures of Al2O3 and TiH2 powders. During sintering, TiH2 decomposed to form metallic Ti. The effects of the Ti content on the mechanical and electrical properties of the composites were then investigated. No Ti‐Al intermetallic compounds were detected by X‐ray diffraction, and energy‐dispersive X‐ray spectroscopy indicated the presence of Al‐Ti‐O solid solution and Ti‐O phases. The composites showed enhanced densification; the measured densities were higher than the calculated theoretical values. Microstructural observation revealed homogeneously distributed fine Ti particles dispersed in the Al2O3 matrix. The Ti particle size ranged from submicrometer to a few micrometers depending on the Ti content. The fracture mode of the composites was primarily transgranular, in contrast to the intergranular fracture mode of monolithic Al2O3. Although the flexural strength was decreased with increase in Ti content, the composite containing 20 vol% Ti displayed the maximum fracture toughness of 4.3 MPa·cm1/2, which was 37% greater than that of monolithic Al2O3. The composites containing more than 15 vol% Ti exhibited drastic decreases in resistivity (~10−1 Ωcm), which were attributed to the formation of interconnected Ti networks at these Ti contents. The percolation threshold volume for electrical conduction in the present system was calculated to be 13.8 vol%. The results indicate that dispersing fine Ti particles into Al2O3 increased the fracture toughness and improved the conductivity of Al2O3.

Performance and fuel cell applications of reacted ball-milled MgH2/5.3wt% TiH2 nanocomposite powders.

The present study aimed to enhance the kinetics behavior and destabilize the thermal stability of MgH2 powder by high-energy milling of Mg powder under 50 bar of H2 for several hours using Ti-balls as the milling media. The results showed a monotonical increase in Ti content worn off the milling media and introduced into the milled powders. This gradual doping led to homogeneous distribution of fine Ti particles into the Mg/MgH2 powder matrix without agglomeration or compositional fluctuations at the micro-level. During the activation stage of the powders, achieved at 350 °C/35 bar H2 prior to hydrogenation kinetics measurements, elemental Ti reacted with H2 to form fine TiH2 particles. Our proposed in situ mechanically induced catalyzation approach was found to be mutually beneficial for decreasing the apparent activation energy of decomposition. In addition, introducing 5.3 wt% of TiH2 to the MgH2 powder obtained after 50 h led to the achievement of superior enhancement of gas uptake/release kinetics at relatively low temperatures. The nanocomposite MgH2/5.3 TiH2 powder possessed fast hydrogenation/dehydrogenation kinetics behaviors and revealed long cycle lifetimes. This system was successfully employed as a solid-state hydrogen source to charge the battery of a cell-phone device using an integrated Ti-tank/commercial proton exchange membrane-fuel cell system.

Fine Ti Powders Through Metallothermic Reduction in TiO2–Mg–Ca Mixtures

Fine Ti powders were prepared through magnesiothermic reduction in TiO2–Mg–Ca mixtures under 4 MPa of Ar followed by acid leaching (with HCl or HNO3) and characterized by XRD, SEM/EDS, and chemical analysis. Thus prepared Ti powders exhibited the specific surface ranging between 7.0 and 30.0 m2/g. The produced Ti powders can find their application in pyrotechnics, powder metallurgy, and as raw material for SHS of inorganic compounds.

Microstructure design of the excellent shape recovery properties in (Ti,Hf)2Ni/Ti-Ni-Hf high temperature shape memory alloy composite

The microstructure, martensitic transformation behaviors, mechanical and shape recovery properties of the (Ti,Hf)2Ni/Ti-Ni-Hf composite fabricated by SPS were investigated. The microstructure of the (Ti,Hf)2Ni/Ti-Ni-Hf composite consisted of B19′ martensite matrix interspersed with (Ti,Hf)2Ni phases. The larger (Ti,Hf)2Ni phases distributed at the surface of the original alloy powders and formed network structure, while the fine (Ti,Hf)2Ni phases was also observed in the interior of the original alloy powders. The distribution and the amount of the (Ti,Hf)2Ni phases contributed to the lower transformation temperatures of the (Ti,Hf)2Ni/Ti-Ni-Hf composite. In addition, the strengthening of larger (Ti,Hf)2Ni phases with the network structure at the macro level and precipitation strengthening of fine (Ti,Hf)2Ni phases at the micro level played an important role in the better mechanical and shape recovery properties in the sintered Ti-Ni-Hf composite.

Microstructural Evolution during Pressureless Sintering of Blended Elemental Ti-Al-V-Fe Titanium Alloys from Fine Hydrogenated-Dehydrogenated Titanium Powder

A comprehensive study was conducted on microstructural evolution of sintered Ti-Al-V-Fe titanium alloys utilizing very fine hydrogenation-dehydrogenation (HDH) titanium powder with a median particle size of 8.84 μm. Both micropores (5–15 μm) and macropores (50–200 μm) were identified in sintered titanium alloys. Spherical micropores were observed in Ti-6Al-4V sintered with fine Ti at the lowest temperature of 1150 °C. The addition of iron can help reduce microporosity and improve microstructural and compositional homogenization. A theoretical calculation of evaporation based on the Miedema model and Langmuir equation indicates that the evaporation of aluminum could be responsible for the formation of the macropores. Although reasonable densification was achieved at low sintering temperatures (93–96% relative density) the samples had poor mechanical properties due mainly to the presence of the macroporosity and the high inherent oxygen content in the as-received fine powders.

Microstructure and mechanical properties of Al2O3/TiAl joints brazed with B powders reinforced Ag-Cu-Ti based composite fillers

In this manuscript, Al2O3 ceramic and TiAl alloy were brazed with Ag-Cu-Ti based composite fillers containing B powder additive. The effects of B content, Ti content, and the brazing temperature on the microstructure and mechanical properties of the brazed joints were investigated. The typical interfacial microstructure of the brazed joint was: Al2O3/Ti3(Cu, Al)3O/Ag(s.s)+TiB+Ti(Cu, Al)+fine AlCu2Ti/blocky AlCu2Ti+AlCuTi/TiAl. TiB whiskers synthesized in situ by the reaction of the B additive with Ti, served as nucleation sites for the formation of fine Ti(Cu, Al) and AlCu2Ti grains and improved the bonding properties. With increasing B content, more fine-grains were formed in the brazing seam and the thickness of the Ti3(Cu, Al)3O reaction layer adjacent to the Al2O3 ceramic decreased. Brazing parameters also influenced the joint microstructure. Growth of Ti3(Cu, Al)3O layer and AlCu2Ti formed with increase in brazing temperature. Moreover, the formation of dispersed fine-grains in the brazing seam depended largely on the initial Ti content in the composite filler. With increase in initial Ti content, the TiB-reinforced area was broadened while the blocky AlCu2Ti content decreased gradually. The maximum shear strength of Al2O3/TiAl joint brazed with B-reinforced composite filler was 148MPa, which was 246% higher than that brazed without B addition. The joint shear strength was determined by the combined influences of the thermal expansion mismatch between the joined materials, the thickness of the Ti3(Cu, Al)3O layer, and the presence of defects in the joints.

Control of hydrogen cracking in the welded steel using microstructural traps

Hydrogen diffusion into steel can embrittle the material in H2S environments, but this effect can be offset by suitable hydrogen trapping sites in the microstructure. Fine Ti(C,N) inclusions have been studied as the trapping sites in high strength low alloy (API X-70) welds, with Ti additions ranging from 0.004 to 0.16 wt.%. The trapping sites were investigated by electron microscopy and thermal desorption spectroscopy. Manganese sulphide particles were the main initiation sites for hydrogen induced cracking as expected. The optimum Ti addition was around 0.02% with no evidence of cracking in the weld. The estimated values of trapping activation energy for dislocations, microvoids, MnS and Ti(C, N) were approximately 25.9, 34.6, 65.1 and 87.6 kJ mol−1, respectively.

Corrosion and Tribocorrosion Behavior of Ti-Alumina Composites

This work focuses in the corrosion and wear properties of titanium reinforced with 1% wt. alumina particles, produced by a combination of colloidal techniques and powder metallurgy. The alumina particles were added to control the grain growth of titanium during sintering, and simultaneously to increase hardness and wear resistance. Colloidal techniques permitted a homogeneous dispersion of alumina particles on the surface of fine Ti particles by the formulation of stable aqueous suspensions that were further processed by spray-dry to obtain spherical granules with improved compressibility. Ti-alumina samples were produced by uniaxial pressing of granules and vacuum sintering leading to materials with homogeneous microstructure, a reduction of grain size higher than 50 % with respect to pure titanium, and a sensible increase in hardness. But the addition of ceramic particles can also have an influence on the corrosion behavior that is one of the most interesting properties of titanium alloys, and on wear resistance, that is one of the drawbacks of Ti. Moreover, the study of simultaneous action of wear and corrosion (tribocorrosion) is an area of highest interest in applications like biomedical or automotive. The corrosion behavior was evaluated by Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarization (PP) in NaCl at two concentrations (0.9 % and 3.5 %) and temperatures (37 oC, and room temperature). Tribocorrosion tests were performed using a reciprocating ball-on-plate tribometer where a 10 mm diameter alumina ball was used as counter material, and 10 N normal load was applied during 30 min in the same concentrations and temperatures of NaCl as in the static corrosion tests. The results showed a clear improvement of wear resistance on the composite without reducing the corrosion behavior in both conditions.