TiB Grains Research Articles

Effect of Ti-B Grain Refiners on Wear and Corrosion of the A332 Alloy with Sr Modification

Grain refiners play a critical role in changing characteristics and properties of casting aluminum alloys. The Al-Si alloy (A332) is one of the most popular hypoeutectic alloys with a large range of industrial applications. It has a varied phase and morphology; however, it features problems with acicular-shaped eutectic phase, and generally exhibits dendritic cast grain type. To change this situation, the Sr element acts as a modifier of eutectic, which, along with a grain refiner may increase mechanical properties. In this work, two different grain refiners (Al5Ti1B, Al5Ti2B) were applied to the A332 alloy modified with Sr, and analyzed in relation to grain size, hardness, corrosion resistance, and wear behavior. Corrosion tests in 3.5 wt.% NaCl solution, nanoindentations, and Heyn’s method to analyze grain size and microhardness as optical and SEM images were made to examine the changes caused by grain refiners. A reduction in grain size was achieved, and the influence in size and hardness of the β-Fe phase was verified in the wear and corrosion analyses.

Refined microstructure and enhanced wear resistance of titanium matrix composites produced by selective laser melting

In order to investigate the effect of TiB2 contents on the microstructure and wear resistance of titanium matrix composites, commercial pure Ti (CP-Ti) powders with 0–7.5 wt.% TiB2 particles were melted by selective laser melting (SLM) to produce the in-situ Ti-TiB composites. When the TiB2 content increases from 2.5 wt.% to 7.5 wt.%, the microstructures of the Ti-TiB composites undergo a transition from the single phase of α′-Ti to the mixed phases of α′-Ti, TiB and TiB2, and the acicular α′-Ti is refined significantly from 1.03 ± 0.24 μm to 0.36 ± 0.05 μm, showing that increasing the TiB2 content induces the formation of TiB and refines the microstructure. Moreover, large TiB2 particles are not melted completely and they react with the Ti matrix liquid to form a TiB layer around the Ti matrix during SLM. However, small TiB2 particles are completely dissolved into the Ti matrix liquid so that the eutectic TiB grains are precipitated at the boundaries of the Ti matrix after in-situ reaction of TiB2 with Ti. The formation of α′ martensite in the titanium matrix and the addition of TiB2 can induce the fine grain strengthening, the dispersion strengthening, the solid solution strengthening in the SLM-produced composites. The results indicate that the microhardness of the composites increases from 258 ± 10.3 HV0.2 to 435 ± 14.7 HV0.2. The wear process of the SLM-produced CP-Ti and TiB2 reinforced Ti matrix composites is accompanied by adhesion wear, abrasive wear and oxidation wear. As a result, when the TiB2 content increases to 7.5%, the wear resistance of the composites increases by 32.6% compared with that of the CP-Ti. These improvements are mainly due to strengthening and hardening effects induced by TiB2 particles and refinement of Ti matrix. This study provides some basis for developing wear-resistant and high-strength titanium alloys.

Characteristics of aluminum AC4B with variations of silicon nitride reinforced composite produced by a stir casting process

At present, the combination of metal matrices and ceramic reinforcement as composite is popular for creating materials with good mechanical properties. Aluminum is used as a matrix because of its lightweight, ductile, and low melting point. In this reserach, the effect of adding silicon nitride on characteristics of Al AC4B is studied. Five sample variations were made based on fraction volume percent (1, 3, 5, 7, 10) which were fabricated through stir casting method. In the fabrication process the magnesium element was added to increase the wettability, TiB grain refiner, and modification with strontium element. The samples made got destructive, tensile, impact, and hardness testing to determine the mechanical properties of the composite. Observation of phases, elements, compounds and microstructure was done to see the distribution of reinforcing particles in the aluminum matrix and the estimated phases formed. The results showed that the optimum tensile strength of variable occurred at the addition of 1% volume of silicon nitride with a strength value of 104.94, and the optimum hardness value was at the addition of 3% Si3N4, which was 44.8 HRB. The phases formed in the composite were Mg2Si, Al2Cu, β-Al5FeSi, and π - Al9FeMg3Si5 phases.

Effect of Al-TiB Addition on the Mechanical Properties and Microstructure of Al-ADC12/NanoSiC Produced by Stir Casting Methods

Addition of Ti-B grain refiner in Al-ADC12/nanoSiC composite results in improvement of tensile strength, hardness, and wear resistance through grain refinement. In this research, composite of Al-ADC12/nano SiC (0.15 %vf) with variations of TiB respectively (0.0), (0.02), (0.04), (0.06), dan (0.08) wt% were produced by stir casting. 10% of Mg were added to promote wettability between reinforce and matrix. It was found the best addition of TiB is 0.04 wt% Ti-B which results 135,9 MPa in tensile strength, 46 HRB in hardness, and 1.47x10-5 mm3/s as wear rate. The increase in mechanical properties of composites mainly because of Al3Ti acts as nucleants which initiates the grain refinement and the existence of MgAl2O4 phase indicates an interphase between nano SiC and ADC12 matrix. However, the increase of Ti-B addition after optimum number gives no significant results. High composition of iron and magnesium addition will form intermetallic phase β-Fe, π-Fe, and Mg2Si.

Microstructures and Crack Propagation in the Joint of Solidified TiC-TiB<sub>2</sub> to Ti-6Al-4V Prepared by Reactive Fusion Bonding in Ultrahigh Gravity Field

By taking combustion synthesis in ultrahigh gravity field to prepare solidified TiC-TiB2 composite ceramic, laminated composite of the ceramic to Ti-6Al-4V was achieved by fusion bonding and atomic inter-diffusion, and within the joint there formed the unique microstructure of multiscale (micrometer-micro/nanometer-nanometer) and multilevel characterized by size and distribution of TiB2 and TiB due to the presence of a series of metallurgical reaction including peritectic reaction of solidified and Ti liquid, direct growth of TiB solids from liquid Ti and subsequent eutectic reaction of TiB solids and liquid Ti. FEMSEM images of crack propagation paths at the joint showed despite the contribution from crack bridging of micro-nanometer TiB2 and TiB platelets to crack propagation resistance, residual stress toughening and subsequent crack pinning by micro-nanometer TiB2 ,TiB platelets and needle-like nanometer TiB grains as well as ductile phase toughening and bridging toughening by Ti metallic phases became the primary resistances to crack propagation, thereby presenting the delayed fracture behavior in the joint, so that shear fracture usually occurred at the solidified Ti alloy rather than the joint, and shear strength of 375 ± 55 MPa was achieved between the solidified ceramic and Ti alloy.

Microstructure and Fracture Behavior of the Joint of Solidified TiB<sub>2</sub> Ceramic with Ti-6Al-4V Achieved by Reaction Fusion Bonding in Ultrahigh-Gravity Field

Based on taking combustion synthesis in ultrahigh-gravity field to prepare solidified TiC-TiB2 ceramic, laminated composite of TiC-TiB2 to Ti-6Al-4V was successfully obtained by fusion bonding, and within the joint there achieved multi-scale (micron-submicron-micro-nano) and multi-level (TiC1-x-TiB-TiB2 + TiB2-Ti-TiC1-x-TiB + TiB2-TiC1-x-TiB-Ti + TiB-TiC1-x-Ti + TiC1-x-Ti + Ti) composite structures characterized by size and distribution of TiB2 and TiB phases. As micro-nano TiB2, TiB platelets and needle-like nano TiB grains at the joint area initiated residual stress toughening and pinning at crack tip, while Ti phases initiated ductile phase toughening and subsequent bridging in crack-tip wake, a typical delayed fracture under external stress was manifested obviously in the joint of TiC-TiB2 to Ti-6Al-4V. As a result, the shear fracture of the joint of ceramic toTi-6Al-4V alloy usually occurred in solidified area of Ti alloy rather than the joint, and the shear strength between the ceramic and Ti alloy was maintained at 375 ± 55 MPa.

Enhancement of TiB Grain Refining Effect on A356 Gravity Die Casting with the Addition of Yttrium

The present work investigates the effect yttrium on the grain refining efficiency of Al-5Ti-1B in gravity die cast A356 aluminum alloy. A series of casting experiments were carried out in which the Ti and B contents were maintained constantly at 0.1 and 0.02 wt% respectively. The inoculation level of yttrium was manipulated at the amount of 0, 0.1, 0.2, 0.3, 0.4 and 0.5 wt%. Microstructural characterization of the as-cast A356 alloy was investigated by means of optical microscope and its phases are detected by XRD. XRF is used to determine the contents of inoculating elements such as Ti, B and Y so that their actual optimal ratio in the casting can be approximated. The mechanical properties tested are tensile strength and hardness. The inoculation of yttrium was found to enhance the grain refinement effect of Al-5Ti-1B grain refiner and improve the mechanical properties. The optimal weight percentage of yttrium was discovered to be 0.3. The grain refining efficiency of combining yttrium and Al-5Ti-1B on A356 aluminum alloy was mainly attributed to the heterogeneous nucleation of TiB2 and TiAl3 particles which were dispersed more evenly in the presence of yttrium and also as a result of α-Al grain growth restriction by AlY3compound precipitated at grain boundaries during solidification.

Effect of Grain Refinement on Residual Strain and Hot Tearing in B206 Aluminum Alloy

Aluminum-copper alloy B206 has an excellent potential for use in automobiles as suspension knuckles and control arms. The main shortfall of this alloy however, is its high susceptibility to hot tearing. Grain refinement has been shown to reduce hot tearing severity in Al alloys. In the present study, Ti-B grain refiner was added at two levels (0.02 and 0.05 wt% Ti) to B206 to investigate the effect on hot tearing. Residual lattice strain was measured for each condition using neutron diffraction. Equiaxed fine grains significantly reduced hot tears in the alloy, and this resulted in a lower magnitude of residual strain along the casting.

Microstructures and mechanical properties of the in situ TiB–Ti metal–matrix composites synthesized by spark plasma sintering process

In situ synthesized TiB reinforced titanium matrix composites have been synthesized by spark plasma sintering (SPS) process at 950–1250 °C, using mixtures of 15 wt% TiB 2 and 85 wt% Ti powders. The effects of the sintering temperature on densification behavior and mechanical properties of the TiB–Ti composites were investigated. The results indicated that with rising sintering temperatures, relative densities of the composites increase obviously, while the in situ TiB whiskers grow rapidly. As a result, bending strength of the TiB–Ti composites increases slowly at the combined actions of the factors referred above. Fracture toughness of the composites is improved remarkably due to the large volume fraction of Ti matrix, the crack deflection, pull-out and the micro-fracture of the needle-shaped TiB grains. The results also suggested that TiB–Ti composite sintered at 1250 °C by SPS process exhibits the highest relative density of 99.6% along with bending strength of 1161 MPa and fracture toughness of 13.5 MPa m 1/2.

In situ reaction synthesis of Ti–TiB composites containing high volume fraction of TiB by spark plasma sintering process

The in situ toughened Ti–TiB ceramic–matrix composites containing high volume fraction of TiB were synthesized by spark plasma sintering technique under a pressure of 50 MPa, with sintering temperature ranging from 1100 °C to 1400 °C and heating rate of 150 °C/min, using Ti and TiB 2 powders. Results indicated that Ti–TiB composites sintered at 1400 °C provided the optimal combination of dense microstructure, well developed lath-shaped TiB grains, and excellent mechanical properties, including the relative density of 99.6%, bending strength of 608 MPa, and a rather high fracture toughness of 9.35 MPa m 1/2. Moreover, the micro-hardness of the composites reaches a relatively high level (18.3 GPa).

Rapid synthesis of Ti alloy with B addition by spark plasma sintering

Abstract The in situ TiB/Ti–4.0Fe–7.3Mo composites were fabricated by plasma spark sintering (SPS) technique using mechanical alloying of Ti, Fe65Mo and B powder. The effects of sintering temperature on densification of the composites and microstructure of the in situ synthesized TiB were investigated using scanning electron microscope (SEM) and transmission electron microscope (TEM). A dense composite was obtained after sintering at 1000 °C for 5 min. Under proper ball milling and SPS conditions in situ TiB reinforced Ti–4.0Fe–7.3Mo composites have been prepared. The in situ TiB showed a typical needle shape grow along [0 1 0] direction. The transverse cross-section of TiB grain is a hexagonal shape with the planes of (1 0 0), (1 0 1) and ( 1 0 1 ¯ ) . The stacking faults in the (1 0 0) plane were observed in the TiB needles.

Self-propagating high temperature combustion synthesis of TiB/Ti composites

Dense TiB/Ti composites were fabricated by Self-propagating High Temperature Synthesis connected with Pseudo Hot Isostatic Pressing (SHS/PHIP). T ads, T c and combustion velocities of the TiB– xTi system decrease with increasing the amount of Ti. The synthesized TiB–Ti cermets mainly consisted of TiB and Ti phases, but TiB 2 phase existed in some products with lower content of metal. Needle-like, rod-like or plate-like TiB grains formed in the microstructure of synthesized TiB– xTi composites. The size of the TiB grains decreased with an increasing amount of metal addition. The hardness and relative density of the synthesized materials are all beyond HRA82 and 94%, respectively. The introduction of Ti into TiB– xTi cermets resulted in a drastic increase in the bending strength, tensile strength, compression strength, fracture toughness and the maximum values were obtained with the addition of 40 wt.%Ti.

Simultaneous synthesis and densification of TiB/ α-Ti(N) composite material by self-propagating combustion under nitrogen pressure

Simultaneous synthesis and densification of TiB/ α-Ti(N) composites from Ti (70 mol%)/ B (30 mol%) powder compacts are achieved by self-propagating combustion under a nitrogen pressure of 5 MPa. Dense composite materials (97.5% of theoretical) exhibit excellent mechanical properties, in which their fracture toughness and bending strength are 7.8 MPa m 1/2 and 640 MPa, respectively. Rodlike TiB grains greatly enhance the mechanical properties.