TiB2 Phases Research Articles

Effects of sintering temperature on the microstructure and mechanical properties of double-hard-phase TiB2–TiC cermets

The mechanical properties and microstructure of double-hard-phase TiB2–25-wt.%-TiC–20-wt.%-CoNi cermets prepared at different temperatures were investigated by performing scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The results showed that the transverse rupture strength, indentation fracture toughness, hardness, and relative density of the cermets reached the maximum values of 1654 MPa, 11.06 MPa m1/2, 90.1 HRA, and 99.42 %, respectively, when the sintering temperature was 1462 °C. Solid- and liquid-phase sintering occurred at temperatures below and above 1354.5 °C, respectively. The cermets were composed of TiB2, TiC, TiB, and CoNi phases when sintered at 1440 °C and below, but the TiB phase disappeared when sintered at 1462 °C and above. Both TiB2 core–(Ti, Co, Ni)B rim and TiC core–(Ti, Co, Ni)C rim structures appeared in cermets sintered at 1440 °C and above. In addition, a few TiC core–(Ti, W)C inner–(Ti, W, Co, Ni)C outer double rim structures were formed. A coherent interface was found between the (Ti, Co, Ni)B rim and TiB2 core. A thin CoNi amorphous metallic layer existed at the interface between the (Ti, Co, Ni)C rim and TiC core. In addition, amorphous CoNi was observed in the interfacial region between the CoNi binder and (Ti, Co, Ni)C rim phase and inside the CoNi binder phase. These multi-interface and core–rim structures resulted in excellent strength and toughness of the cermets.

Microstructure and phase composition of Ti-coated cBN powders intended for active coating technology (ACT) processes

Development of an active coating technology (ACT) was aimed at fabricating high strength sinters using metallized powders like in case of titanium coated cubic boron nitride (cBN). It helps to avoid inhomogeneity in distribution of the binder phase during their mixing, being the main defects in such compacts. The information concerning phase composition of the coating formed over cBN during their metallization would be of much help as it concerns setting a proper sintering temperature securing both durable fusion of boride particles and elimination of porosity. Presently, two commercial Ti coated cBN powders are available, i.e. CBN-B-TA, 6–12 µm, from Van Moppes, Switzerland and CeraMicron CM-CBN 80 Ti, 20–30 µm, from Ceratonia, Germany (coded as cBN-VM and cBN-CM, respectively). The present investigation was aimed at characterization of the coatings microstructure and phase composition, being necessary for optimising sintering procedure. The scanning and transmission electron microscopy observations backed with energy dispersive X-ray microanalysis (SEM/TEM/EDS) showed that the cBN-VM particles carried a coating of thickness varying from 50 nm to 150 nm consisting of TiB and TiN phases, while the cBN-CM ones were covered by a much thicker (∼500 nm) coating built of mostly of TiB and TiN2-type crystallites. As the columnar nitride phases formed bulk of the coatings, though at the coating/cBN substrate boundary a nano-crystalline layer of TiB phase was documented in both powders. The crystallites of boride phase were accompanied by a strings of porosity. The XRD measurements indicated also presence of small amounts of the α-Ti(N) phase, which was probably intermixed with the other phases without forming a separate sub-layer. The thinner coating, i.e. one that formed over cBN-VM powder, was contaminated with Cl and K being a residue from the molten salts synthesis (MSS) deposition, as well as some surface oxides. The gathered information makes a basis for elaboration of new generation of cBN sinters of improved properties.

Optimization and characterization of boric acid powder mixed electrical discharge machining of Ti-6Al-4V ELI

The powder mixed electrical discharge machining (PMEDM) process is used for enhancing machining efficiency and improving the surface characteristics of the workpiece compared to normal EDM. The present study evaluates the effect of boric acid powder mixed in deionized water in PMEDM of Ti-6Al-4V ELI (extra low interstitial). The PMEDM process is assessed by evaluating material removal rate (MRR) and surface roughness (SR) at varying powder concentration (PC), current and pulse duration ( Ton). Boric acid PMEDM exhibits advantageous for both MRR and SR, where MRR increases and SR decreases with an increase in PC. To simultaneously achieve higher MRR and lower SR, the grey-fuzzy logic method is employed. Initially, the raw input data is normalized into grey numbers and a single index is obtained through grey relational analysis. Subsequently, triangular membership functions are assigned to the inputs and output. Fuzzy logic rules are then formulated, and grey fuzzy relational grade (GFRG) is calculated for each condition. The optimum condition (GFRG = 0.787) is attained at 15 g/l PC, 9 A current and 106 µs Ton, resulting in a 63% improvement compared to the initial condition. At the optimum condition, MRR increased by 145% and SR decreased by 29% compared to the initial condition. The effect of boric acid in PMEDM can be visualized through the formation of smooth surfaces, exhibiting reduced SR, smaller and shallower craters, and fewer debris and globules. Additionally, the boric acid PMEDM experiments resulted in the formation of a hard TiB phase on Ti-6Al-4V, thus improving its wear resistance.

Effect of Al-5Ti-1B refiner content on the microstructure and mechanical properties of V-x(Al-5Ti-1B) alloys for hydrogen purification

Effect of Al-5Ti-1B refiner content on the microstructure and mechanical properties of V-x(Al-5Ti-1B) alloys manufactured by vacuum arc melting for hydrogen purification has been investigated in this work. Significant changes appeared in the grain morphology of V-xATB (x=2, 3, 4, 5) alloys with the Al-5Ti-1B (ATB) content increasing (2–5 wt%), while slender needle-like TiB phases were gradually precipitated inside the grains and increased in quantity, and grains were gradually refined. The precipitation of TiB phases in V-xATB alloys is advantageous for grain refining. Forming reasons of TiB phase and its morphology were discussed. The fracture mode for all five alloys is brittle fracture at room temperature. The combined strengthening effect of solid solution, fine-grained and precipitation of V-xATB alloys gradually improve with increasing ATB content, increasing the alloys' hardness and strength. The hardness and strength of the V-5ATB alloy are the highest, but the elongation is lower despite the fact that the grain size is the smallest among V-xATB alloys. This is because the extent of plasticity increase caused by grain refinement in the V-5ATB alloy is less than the extent of plasticity decrease caused by the strengthening of solid solution and hard-brittle TiB phase precipitation. This can be attributed to the significant reduction in plasticity caused by the solid solution and hard-brittle TiB phases precipitation of V-5ATB alloy.

Effects of TiB2 contents on the microstructure and oxidation behavior of Mo-Si-B composite coatings

A novel Mo-Si-B-TiB2 composite coating was prepared on Nb-Si based ultrahigh temperature alloy by slurry sintering. The effects of TiB2 contents (1, 3, 5 and 10 wt%) on the microstructure and oxidation behavior of Mo-Si-B composite coatings were revealed. The results show that TiB2 modified Mo-Si-B composite coatings display a bilayer structure, in which the outer layer is composed of MoSi2, Mo5Si3 and TiB2 phases, and the inner layer is composed of (Ti,Nb)5Si4, (Nb,X)5Si3 and (Nb,Ti)B2 phases. The added TiB2 particles are evenly distributed in the outer layer of the coatings. By introducing TiB2 into the coating, the service life of Mo-Si-B composite coatings is extended from 50 h to 100 h at 1250 ℃, the oxidation rate of the coating is reduced from 1.62 to 0.02 mg2 cm−4 h−1. This indicates that the addition of appropriate TiB2 effectively slows down the oxidation rate and significantly improves the oxidation resistance of Mo-Si-B composite coatings. The Mo-Si-B composite coating with 3 wt% TiB2 had the lowest mass gain (3.9 mg/cm2) after oxidation at 1250 ℃ for 100 h, and it exhibited the best oxidation resistance. This is attributed to the formation of composite oxide scale with crack-free, good healing ability, suitable levels of differential thermal expansion and low oxygen permeability.

Evolution of microstructure and mechanical properties of TiB2-7.5 wt.% WC-based cermets sintered at different temperatures

The evolution of microstructure and mechanical properties of TiB2–7.5 wt% WC-based cermets sintered at different temperatures were investigated. The results showed that eutectic liquid phase appeared at around 1335 °C, indicating that solid-phase sintering occurred below that temperature, while liquid-phase sintering occurred above that temperature. TiB2, W2CoB2, WB and CoNi phases were detected in the XRD patterns of cermets sintered at different temperatures, and TEM analysis showed the presence of TiC phase. So the following chemical reaction should occur: TiB2 + WC + Co → W2CoB2 + WB + TiC. The TiB2 core - (Ti, W, Co, Ni)(B, C) rim phase were observed in the cermet sintered at 1397 °C. As the increase of sintering temperature, the solubility of WC and TiB2 in CoNi binder phase, and the number of core-rim structure hard phase particles increased. The formation of core-rim structure enhanced the interfacial bonding strength between TiB2 phase and CoNi binder, which was beneficial for improving the strength and toughness of cermets. The cermets sintered at 1465 °C had good comprehensive mechanical properties, with a relative density of 99.62%, a hardness of 17.34 ± 0.43 GPa, a transversal rupture strength of 2038 ± 53 MPa, and an indentation fracture toughness of 12.15 ± 0.32 MPa·m1/2.

Microstructure, mechanical properties and cutting performance of CVD Ti(B,N) coatings

TiB0.19N1.06, TiB0.70N0.66, and TiB1.23N0.19 coatings were deposited on cemented carbide via the chemical vapor deposition (CVD) method based on the calculated phase diagrams of the Ti–B–N system. The microstructures, mechanical properties and cutting performances of the Ti(B,N) coatings were systematically studied via X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), nanoindentation, etc. The coating compositions obtained via thermodynamic calculations show the same trend as the experimental values. The XRD and selected area electron diffraction (SAED) results of the coatings reveal that the phase assemblages transform from a dominant cubic structure of TiB0.19N1.06 to a hybrid of cubic and hexagonal structure of TiB0.70N0.66 and finally to a dominant hexagonal structure of TiB1.23N0.19. According to the XPS results, the TiB0.19N1.06 and TiB0.70N0.66 coatings consist of the crystalline phases TiN and TiB2 as well as amorphous BN and TiB, and the TiB1.23N0.19 coating mainly consists of the crystalline phases TiB2 and TiN. The hardness values of the TiB0.19N1.06, TiB0.70N0.66, and TiB1.23N0.19 coatings are 33.6, 35.1, and 39.1 GPa, respectively. The content of amorphous phase in the Ti(B,N) coatings decreases while the hardness increases as the B content increases and N content decreases. The TiB0.19N1.06 coating exhibits a composite structure of nanocrystallite embedded in amorphous matrix. The TiB1.23N0.19 coated tool prepared in this study demonstrates excellent performance in milling titanium alloy TC18 with a long cutting life up to 56.1 min, an increase of ∼9 % and ∼28 % compared to the TiB1.98 coated tool and commercial grade deposited with CVD TiB2 coating, respectively.

Effect of Al-Ti-B-Er on the Microstructure and Properties of Ultrahigh-Strength Aluminum Alloy

To refine the grain size and improve the mechanical properties of ultrahigh-strength aluminum alloy (Al-10Zn-1.9Mg-1.6Cu-0.12Zr), the Al-Ti-B-Er grain refiner was prepared by the melt reaction method using the aluminum melt and Al + Ti + B precursor. The results exhibit that the Al-Ti-B-Er grain refiner is mainly composed of a block TiAl3 phase, and loose agglomerated nano-sized TiB2 and Al3Er phases. The microstructure of ultrahigh-strength aluminum is significantly affected by the Al-Ti-B-Er refiner, which changes from dendrite to equiaxial grain with increasing Al-Ti-B-Er content, and the size of the eutectic phase is significantly refined. The high-efficiency refinement of Al-Ti-B-Er is due to Er promoting the uniform distribution of TiAl3 particles and the formation of loose agglomerated nano-sized TiB2 particles. The optimal addition content of Al-Ti-B-Er into ultrahigh-strength aluminum alloys is 1 wt%, whose grain size is approximately 40 µm. Additionally, the strength and ductility of ultrahigh-strength aluminum alloys are simultaneously improved by adding 1wt% Al-Ti-B-Er after the T6 treatment, reaching 756 MPa and 20%, respectively. This enhancement in strength and ductility is mainly attributed to grain refinement and the eutectic phase refinement.

Influence of scanning speed on titanium alloy processed with TC4+Ni60/hBN composite powder by laser metal deposition coating technology

PurposeRegarding the broadening of the titanium alloy application field, the surface treatment coating of TC4 alloy has become an essential global research topic. This study aims to illustrate the titanium-based composite coating is created by laser cladding TC4+Ni60/hBN composite powder onto the surface of the TC4 alloy.Design/methodology/approachDifferent laser scanning speeds were initially selected to prepare TC4+Ni60/hBN titanium-based composite coating on the surface of TC4 alloy using RFL-C1000 Raycus fiber laser. Second, the cladding layers with different laser scanning speeds are composed of Ti2Ni, TiN0.3, TiC, TiB, α-Ti and other phases. Finally, precision balances, friction and wear testing machines were used to analyze and test the structure, phase, hardness, wear amount and friction coefficient of the composite coating and to study the effect of laser scanning speed on the microstructure and properties of the titanium-based composite coating.FindingsIt is evident that at the low laser scanning speed, the reinforcing phase agglomeration area is distributed in the substrate as a network. Increasing the laser scanning speed can reduce the cladding layer's friction coefficient and improve the cladding layer's hardness and wear resistance. But too high a laser scanning speed will cause defects such as pores and cracks in the cladding layer and also affect the cladding layer. The bonding performance of the layer and the substrate is optimal in this research at a laser scanning speed of 10 mm/s.Originality/valueThis research has practical value in improving the quality of surface treatment coating in modern aerospace and automotive companies.

Enhanced mechanical/electrical properties of in situ synthesized SiC-TiB2 ceramic composites by reactive hot-pressing sintering

In this work, in situ formed TiB2-reinforced SiC ceramic composites were prepared by reactive hot pressing using SiC, TiC, B4C, and Si as raw materials. Phase composition, microstructure, and mechanical as well as electrical properties were investigated. The formation of the TiB2 phase could be realized from the reaction among TiC, B4C, and Si. In the sintered SiC–TiB2 ceramic composites, the content of α-SiC decreased while that of the in situ formed TiB2 increased. In addition, residual Si only existed in the SiC–TiB2 ceramic composites with in situ TiB2 below 20 mol%. Notably, the comprehensive performance of the SiC–TiB2 ceramic composites was enhanced with the increase of TiB2 content due to the reduction of pores and residual Si. Finally, nearly fully dense SiC–TiB2 ceramic composites were obtained when in situ formed TiB2 was above 20 mol%. The SiC–TiB2 ceramic composites, with in situ TiB2 of 30 mol%, exhibited hardness of 26.9 ± 2.3 GPa, fracture toughness of 6.83 ± 0.6 MPa m1/2, and electrical resistivity of 0.3 mΩ cm, respectively.

The microstructure and mechanical properties of steel-bonded TiB2 modified by adding Mo2C

In this study, the microstructure and interface of steel-bonded TiB2 were adjusted by adding Mo2C, so as to improve its comprehensive mechanical properties. The addition of Mo2C led to the formation of two kinds of core-rim structures, including TiB2 core-(Ti, Fe, Ni, Cr, Mo)B rim, and TiC core-(Ti, Fe, Ni, Cr, Mo)C rim. Micro - nano scale of TiB2, TiC and (Mo, Cr)C particles were formed in the steel-bonded TiB2. The introduction of Mo element caused the redistribution of elements in Fe-based binder phase, and two types of binder phases were generated, one was Ni-rich binder phase, and the other was Cr-rich binder phase. A full coherent interface was formed between the core and rim phase, and the amorphous metal thin layer was formed between the rim and binder phase. A coherent interface was formed between TiB2 and (Mo, Cr)C phase, (Mo, Cr)C and Ni-rich binder phase, as well as TiB2 and Ni-rich binder phase. Both the coherent interface and amorphous metal thin layer greatly enhanced the interface bonding strength, and improved the strength and toughness of the steel-bonded TiB2. The steel-bonded TiB2 with 6.0 wt% Mo2C exhibited excellent comprehensive mechanical properties, and its relative density, hardness, transverse rupture strength and fracture toughness were 99.94 ± 0.06%, 92.3 ± 0.5 HRA, 1278 ± 37 MPa and 10.90 ± 0.28 MPa·m1/2, respectively.

Microstructural, mechanical, and biocompatibility properties of Ti–Cu/B4C composites for biomedical applications

This study investigated the effects of B4C on the microstructural, mechanical, and biocompatibility properties of Ti–Cu/B4C composites produced by powder metallurgy. Different amounts of B4C (3, 6, 9, and 12 %) were added to the Ti–Cu matrix. XRD results showed that Ti2Cu, α-Ti, TiB, and B4C phases formed in the microstructure. The addition of B4C and the phases forming in the microstructure resulted in significant increases in the hardness and wear resistance of the composites. SEM images of the wear surfaces showed that the abrasive wear mechanism was dominant. Biodegradability analyses showed that sodium, found in trace amounts in the structure of the alloys, and calcium, released from the structure of B4C into the medium, were the least at the addition of 6 % B4C. Considering the reduced amount of phosphate in the medium, it was found that the mass gain observed in the specimens was due to the deposition of calcium-phosphate precipitates on the surface of the composites. This result suggested that Ti–Cu/B4C alloys were bioactive for bone and may provide osteointegration. Indirect MTT analysis with bone marrow mesenchymal stem cells showed that the specimens were cytotoxic at an acute dose on the first day. However, the cytotoxic effect diminished when they were kept in the PBS medium and replaced every other day for 28 days. Notably, the composite specimen with the addition of 6 % B4C demonstrated maximum cytocompatibility. Consequently, it indicated that adding B4C to the alloy improved osteogenic properties, although it partially increased copper release into the medium.

Study on the microstructure and properties of TiB2-CoCrFeNiW0.2 metal ceramic composites prepared by pressureless sintering

Three types of TiB2-HEA ceramic composite were prepared using a non-equimolar ratio CoCrFeNiW0.2 high entropy alloy (HEA) as a binder, mechanical alloying (MA), and 1600 °C pressureless sintering (PS) processes. The phase analysis results indicate the presence of TiB2, FCC, and TCP phases in the TiB2-HEA composite. A detailed study was conducted on the microstructure of TiB2-HEA composite. The results indicate that there is a certain solid solubility between TiB2 and HEA. The Ti and B elements in TiB2 will enter HEA, and the elements in HEA will also enter TiB2. Along with the discovery of many lattice distortion regions in TiB2, a diffraction pattern of P-43m cubic structure was also observed in HEA. HEA has good wettability with TiB2, so it can not only inhibit the grain growth of TiB2, but also improve the performance of TiB2-HEA composite by utilizing the inherent excellent properties of HEA. There are both intergranular and transgranular fractures in the TiB2-HEA composite. The relative density, flexural strength, Vickers hardness, fracture toughness, and electrical resistivity of TiB2-30 wt%HEA are 99.7%, 680 MPa, 18.6 GPa, 6.4 MPa m1/2, and 5.7 × 10−7 Ω m, respectively.

Microstructure and anti-ablation of laser cladding Ti-Zr-B-C coating on TC11 titanium alloy

To enhance the service life and application range of titanium alloys in the aerospace sector, Ti-Zr-B-C coatings with varying B4C contents (0–30 wt%) on TC11 titanium alloy was fabricated by laser cladding. The microstructure and anti-ablation were investigated in the present work. The results show that the whisker-like TiB phases and granular TiC and ZrC phases were observed in the coatings due to the in-situ reactions. With increasing the content of B4C, the number of reinforcing phases in the coating increased and distributed uniformly, resulting in the improvement of the microhardness up to 803.8HV. Furthermore, due to the formation of TiO2-ZrO2-B2O3 dense multiphase oxide layer on the surface during the ablation process, the coating with 20 wt% B4C exhibited the best anti-ablation at 1400ºC, the mass ablation rate (MAR) and linear ablation rate (LAR) were −2.62 mg/s and 3.67μm/s, respectively, which were just 62.8 % and 50.07 % in comparison with the substrate. This is mainly attributed to the formation of TiO2-ZrO2-B2O3 layer is beneficial to reduce the infiltration of O2 and the evaporation of liquid B2O3, leading to the excellent anti-ablation.

Toughening mechanism of B4C/TiB2 ceramic materials by in situ reaction via spark plasma sintering

AbstractTo enhance the fracture toughness of B4C ceramics, B4C/TiB2 ceramics with excellent performance were prepared by using TiO2 as the addition item and using spark plasma sintering to introduce TiB2 based on in situ reaction, which was compared with ceramics directly introduced with TiB2, the impacts of TiO2 content, temperature and holding time on B4C/TiB2 ceramics were studied, and the toughening mechanism of B4C/TiB2 ceramics in situ reaction was discussed. The results showed that compared with the ceramics directly introduced with TiB2, B4C/TiB2 ceramics with reinforcement phase TiB2 introduced through in‐situ reaction were easier to obtain higher relative density and better properties. Due to the existence of a discharge effect and the application of pulse current, B4C/TiB2 ceramics with excellent comprehensive properties can be prepared at lower temperatures and short time. When 15 vol% TiO2 was added, the temperature was 1750°C and the holding time was 10 min, the comprehensive properties were better, and their relative density, Vickers hardness, flexural strength, and fracture toughness were 98.5%, 27.72 GPa, 474 MPa, and 5.08 MPa·m1/2, respectively. Toughening mechanisms such as crack deflection, crack branching, and crack bridging improved the fracture toughness.

Effects of sintering temperature on the microstructure evolution and mechanical properties of TiB2-20 wt% CoNi cermets

Microstructure evolution and mechanical properties of TiB2-CoNi cermets at different sintering temperatures were investigated. A small amount of liquid phase appeared between 1362 ºC and 1398 ºC. Solid phase sintering mainly occurred below this temperature range, while liquid phase sintering mainly occurred above this temperature range. At around 1460 ºC, dissolution and re-precipitation occurred around TiB2 particles due to liquid phase migration. Only TiB2 and CoNi phases were detected on XRD patterns at different sintering temperatures. As the sintering temperature increased, the relative density, fracture toughness, transverse fracture strength, and hardness of cermets increased, while their porosity decreased. The main influencing factors on the properties of cermets sintered at 1460 ºC and above were the interface bonding strength and the grain size, while the porosity was the main influencing factor for cermets sintered below 1460 ºC.

Anti-fading study of Al–Ti–B by adding Ce on 6111 aluminum alloy

It is a practically significant issue to overcome the low efficiency and the short action time of Al–Ti–B master alloy for the grain refinement of aluminum alloys. In this paper, the phase relationship of the Al–Ti–B–Ce system, the effect of rare earth elements on the evolution of the morphology of the refining phases TiB2 and Al3Ti, and the effect of the refiners on the microstructure and properties of the 6111 alloy are investigated. The experimental results show that the addition of rare earths introduces the rare earth phase Ti2Al20Ce into Al–Ti–B. The rare earth phase acts as an effective protective shell, reduces the free energy of Al3Ti, prevents further movement at the Solid/Liquid interface, and inhibits the aggregation and growth of the Al3Ti phase. By adsorbing on the surface of the TiB2 phase, the rare earth reduces the surface energy and size of the TiB2 phase, thus reducing the possibility of agglomeration. The fine and dispersed refining phase results in more effective nucleation sites in the melt, which can maintain grain refining for a long time and has better anti-fading effect. Therefore, the grain refiner Al–5Ti–B + Ce can effectively refine the grain of 6111 alloy, reduce the grain refinement fading shortcoming, and improve the strength and ductility of 6111 aluminum alloy.

A Study of the Superplastic Deformation Behavior of Low-Cost Ti-2Fe-0.1B Alloys.

Titanium alloys have high specific strength and corrosion resistance, which have promising applications in industry. However, the machinability of titanium alloys is limited due to their crystal lattice and physical properties. Thus, in recent years, the superplastic forming of titanium alloys has been intensively developing, in particular, forming at low temperatures and/or high strain rates. In this work, a tensile test of low-cost Ti-2Fe-0.1B alloys was carried out at a temperature of 550~750 °C and a strain rate of 1 × 10-3 s-1~1 × 10-2 s-1. The results showed that the alloy exhibited good superplasticity even at a high strain rate (1 × 10-2 s-1) and a low deformation temperature of 550 °C; the elongation of the alloy in this state reached 137.5%. The high strain rate sensitivity coefficient m (0.3) and the maximum elongation (452%) were obtained at a strain rate of 1 × 10-3 s-1 and a temperature of 750 °C. Characteristics of the microstructure showed that during superplastic deformation, the recrystallization and grain boundary sliding of the alloy phases were accelerated, which could be ascribed to the effect of the element Fe. At the same time, the TiB phase located around the primary elongated α grains could also induce dynamic recrystallization and dynamic globularization during deformation.

Heterogenous Grain Nucleation in Al-Si Alloys: Types of Nucleant Inoculation

The objective of the current work is to establish, on the one hand, the conventional mechanisms of grain refining and, on the other hand, the effect of the refining-modification interaction in Sr-modified Al-Si alloys on the achieved grain refining and the modification of eutectic silicon. For this purpose, the hypereutectic alloy A390.1 (~17%Si) was used. Various grain refiners were used, namely, Al-10%Ti, Al-5%Ti-1%B, and Al-4%B. After the preparation of the liquid metal, several concentrations of these master alloys were added to the liquid bath according to the desired objective. The different melts prepared were heated at 750 °C and cast in a preheated graphite mold with a solidification rate of around 0.8 °C/s. The liquid metal was. The presence of strontium (added in the form of Al-10%Sr master alloy) and boron completely affects the microstructure of the alloy. An atom of Sr unites with 6 atoms of B to form a compound whose stoichiometric formula is of the SrB6 type, leading to a significant reduction in the modification. A strong relationship exists between the addition of B and the recovery level of Sr. The affinity between titanium and boron is stronger than the affinity between boron and strontium. Both B and TiB2 phase particles do not react with Si; it is only the Ti part of the Al-Ti-B master that forms (Al, Si)3Ti. Regardless of the amount of Si content in the alloy, the Al-4%B master alloy achieves the best grain refining compared to Ti-containing master alloys.

Strength-toughness matching mechanisms of a boride-reinforced Ti6Al4V compositionally graded material fabricated using spark plasma sintering

In this work, an in-situ boride-reinforced Ti6Al4V compositionally graded material was prepared successfully by spark plasma sintering (SPS), and exhibited a good potential for military application because of its stepwise transition properties from a high-toughness end to a high-strength end along the thin-thickness direction. Microstructure characterization shows the chemical gradient ranged from 0 to 30 wt% TiB2 along the thickness direction, which was correlated with increasing micro-hardness values ranging from 565±5HV to 1270±5HV, respectively. The strength-toughness matching mechanisms of the gradient composites with different compositional gradients were discussed based on the static compression experiments and the dynamic Hopkinson compression rod experiments. The primary phases of the gradient composites included the α-Ti phase, β-Ti phase, remained TiB2 and in-situ formed whisker-like TiB phases. The composites with a compositional gradient of G84 (0, 0, 15, 30 wt%) exhibited the best impact resistance which achieved a good balance of high toughness and strength, and exhibited a compressive strength of 2148±5 MPa and a good elongation of 20 ± 0.5%. The strength-toughness matching mechanisms can be explained by the dispersion strengthening effect due to the presence of the in-situ formed TiB phase, and the consumption of more fracture energy by dislocation defects, which can prevent the crack propagation. Moreover, the pull-out of the whisker-like TiB phases toughened the gradient composites furthermore. This research demonstrated a reliable method for preparing TiB2/Ti–6Al-4Vgradient composites with high-impact resistance.