TiB2 Composites Research Articles

Mechanical behavior of porous commercially pure Ti and Ti–TiB composite materials manufactured by selective laser melting

Commercially pure titanium (CP-Ti) and Ti–TiB composite parts with three different porosity levels (i.e. 10%, 17% and 37%) were produced by selective laser melting (SLM). Scanning electron microscopy (SEM) investigations show that martensitic (α′) microstructure exists in SLM-processed CP-Ti parts, whilst SLM-processed Ti–TiB composites present needle-shape TiB particles distributed in α-Ti matrix. Mechanical properties of these porous samples decrease with porosity level increasing. The yield strength and elastic modulus of porous CP-Ti parts range 113–350MPa and 13–68GPa respectively, which are much lower than those for porous Ti–TiB counterparts (234–767MPa and 25–84GPa respectively) mainly due to the strengthening effect induced by TiB particles in Ti–TiB samples. Compression stress–strain curves of 37% porous CP-Ti parts show a typical three-stage behavior of ductile porous metals. Also, the elastic moduli of both 37% porous CP-Ti and Ti–TiB samples are similar to that of human bone. SEM investigations of the porous CP-Ti samples after compression testing show that no crack presents until 50% compressive strain and most of deformation is absorbed by porous areas. In contrast, μ-CT investigations indicate that all porous Ti–TiB samples fail at early stages of compression testing due to cracks resulting from insufficient ductility of struts of porous areas, because they are not able to accommodate high strains of the deformation at high strengths.

Microstructure and mechanical properties of AlMgB14–TiB2 associated with metals prepared by the field-assisted diffusion bonding sintering process

AlMgB14–TiB2 composites were prepared using the field-assisted diffusion bonding sintering process (FDB) at 1400°C under a pressure of 50MPa for 8min, and then bonded to Nb and Mo plates. The microstructure of the bonded joints was analyzed using SEM, EDS and XRD techniques, allowing for the phase composition and elemental distribution characteristics of the joint interface to be studied. The shear strength and wear properties were also investigated. The results show that AlMgB14–30wt.% TiB2 composites can be strongly bonded to Nb and Mo metals, forming dense uniform diffusion layers, with an average width above 200μm. The shear strength of the Nb joints is higher than that of the Mo joints. The results from XRD analysis indicate that the main phase of the fractures of the AlMgB14–TiB2+Nb and the AlMgB14–TiB2+Mo is MoB4 and NbB2, respectively. The wear test results show that AlMgB14 decomposes into AlMg2O4 and Al2O3 at 600°C, which can influence the friction and wear properties of AlMgB14–TiB2 composites.

Effect of Ni addition on the preparation of Al2O3–TiB2 composites using high-energy ball milling

Al2O3–TiB2 composites were synthesized using high-energy ball milling from starting powders containing Al, TiO2, and B2O3. To explore the effect of the addition of another ductile metallic phase during milling, 15 wt.% Ni was added to a sample of the starting powders. The phase transformations and microstructure of the milled powder mixtures were investigated using X-ray diffraction and electron microscopy. The results showed that the Ni addition facilitated the mechanochemical reaction between the Al, TiO2, and B2O3. Before the appearance of the Al2O3–TiB2 composite, the intermediate product NiAl was formed by a gradual exothermic reaction. With continued milling, the final phases of Al2O3–TiB2 and Ni were obtained.

Impact response of TiB2–TiB composites

TiB2–TiB composites with a TiB2 content that varied between 100 and 36 wt% were synthesized from TiB2 and Ti powder mixtures by the Spark Plasma Sintering (SPS) technique. The residual porosity, microstructure, phase composition and static mechanical properties of the composites (bending strength, hardness and fracture toughness) were determined using standard characterization techniques. The impact response of the composites has been studied in two series of planar impact experiments. In the first, the samples were shock loaded to an ultimate compressive stress of about 25 GPa in order to determine the materials Hugoniot elastic limit (HEL). In the second series, the composites were shock loaded by a modest, 3–4 GPa, compressive pulse with the purpose to define their spall strength.The experimental results show that both the static and the dynamic properties of the composites reflect their microstructure, residual porosity and phase composition, namely, the TiB2 fraction in the composites. Even a limited Ti addition (5 wt%) in the starting mixture allows to synthesize by an SPS process at a relatively low temperature (1550 °C), composites with elevated mechanical properties, in particular high hardness (∼2400 HV). The addition of 50 wt% of Ti (36 wt% of TiB2 in the composites) yields fully dense composites with a high fracture toughness (∼9.0 MPa m0.5). The wide range of the static and dynamic properties of the TiB2–TiB composites allows their tailor-design to specific applications.

A criterion to identify sinking-in and piling-up in indentation of materials

The instrumented indentation test is usually used to determine the mechanical properties of materials. Depending on the nature of the material, the way the matter flows under the indenter by piling-up or sinking-in affects the calculation of these mechanical properties. Consequently, corrections proposed by Oliver and Pharr and Loubet et al. should be done according to these two behaviors in addition to other corrections associated with the indenter tip defect as well as the compliance of the instrument. In this work we tested different materials having supposedly piling-up or sinking-in behavior: low-carbon steel, aluminum, brass, copper, beta tricalcium phosphate (β-TCP) bioceramic, rolled or sintered stainless steel and ceramic composite TiB2–60% B4C by using two types of indenter, i.e. Vickers and Berkovich ones. From the corrected load–indenter displacement curve, we showed that a criterion, defined as the ratio between the residual indentation depth and the maximum indentation depth reached at the maximum load, is able to identify the predominant deformation mode. For materials for which this ratio is higher than 0.83 piling-up prevails while it is sinking-in when it is lower than 0.83. When the ratio equals 0.83, the two modes of deformation should coexist since the calculations made using either correction of Oliver and Pharr or Loubet et al. give the same results. This novel way of considering the instrumented indentation measurements renders more accurate the determination of the hardness and the elastic modulus since the observation of the indent is then not required for identifying the deformation mode which affects the contact area calculation.

Effects of Forming Conditions and TiC–TiB2 Contents on the Microstructures of Self-Propagating High-Temperature Synthesized NiAl–TiC–TiB2 Composites

The NiAl–TiC–TiB2 composites were processed by self-propagating high-temperature synthesis (SHS) method using raw powders of Ni, Al, Ti, B4C, TiC, and TiB2, and their microstructure and micro-hardness were investigated. The TiC–TiB2 in NiAl matrix, with contents from 10 to 30 wt%, emerged with the use of two methods: in situ formed and externally added. The results show that all final products are composed of three phases of NiAl, TiC, and TiB2. The microstructures of NiAl–TiC–TiB2 composites with in situ-formed TiC and TiB2 are fine, and all the three phases are distributed uniformly. The grains of NiAl matrix in the composites have been greatly refined, and the micro-hardness of NiAl increases from 381 HV100 to 779 HV100. However, the microstructures of NiAl–TiC–TiB2 composites with externally added TiC and TiB2 are coarse and inhomogeneous, with severe agglomeration of TiC and TiB2 particles. The samples containing externally added 30 wt% TiC–TiB2 attain the micro-hardness of 485 HV100. The microstructure evolution and fracture mode of the two kinds of NiAl–TiC–TiB2 composites are different.

Friction and Wear Behavior of AlMgB14–TiB2 Composite at Elevated Temperature

In this article, field-activated and pressure-assisted synthesis was employed to synthesize an ultra-hard, super-abrasive AlMgB14–TiB2 composite ceramic. The friction and wear performance of the AlMgB14–TiB2 composite were evaluated in ambient air at temperatures up to 800 °C by using a reciprocating ball-on-disk high-temperature tribometer. X-ray diffraction experiments were performed to study the crystal structure of worn surfaces of AlMgB14–TiB2 specimens at various temperatures. Scanning electron microscopy and energy dispersive analysis were used to examine the worn surface features and chemical composition of the AlMgB14–TiB2 composite, respectively. Results showed that the friction coefficient of the AlMgB14–TiB2 composite ranged from 0.45 to 0.55 below 300 °C, while the data obtained at 500 and 600 °C were about 0.65. The damage mechanism is transformed from mild abrasive damage at room temperature to adhesive wear at elevated temperature. In the case of 800 °C, the AlMgB14–TiB2 composite exhibited the lowest friction coefficient as the formation of a lubricious oxide film on the wear track.

Structurization of Composites from Self-Fluxing Alloys with Titanium Diboride Additions

The structurization and phase interaction during sintering of the Ni–Cr–B–Si–C–TiB2 composite are studied. X-ray diffraction, scanning electron microscopy, electron microprobe analysis, and metallography are used to examine the effect of 10–40 wt.% titanium diboride additions on the structure and phase composition of the material and powders for thermal spray coatings. It is established that titanium diboride additions lead to the formation of new complex Cr(Me)23C(B)6 phases with microhardness 18–19 GPa and TiC phase. The size and content of these phases can be controlled by changing the amount and size of additions and sintering conditions. The optimum amount of TiB2 promoting high service properties is 20 wt.%. The new phases formed in the composite constitute 30 vol.% and their size is between 1 and 20 μm. It is possible to control the service properties of Ni–Cr–B–Si–C–TiB2 composites and thermal spray coatings by changing the structural and phase composition of the powder material.

Microstructure-hardness-fretting wear resistance correlation in ultrafine grained Cu–TiB2–Pb composites

The retention of the desired combination of mechanical/tribological properties in ultrafine grained materials presents important challenges in the field of bulk metallic composites. In order to address this aspect, the present work demonstrates how one can achieve a good combination of hardness and wear resistance in Cu–Pb–TiB2 composites, consolidated by spark plasma sintering at low temperatures (<500°C). Transmission electron microscope (TEM) studies reveal ultrafine grains of Cu (100–400nm) with coarser TiB2 particles (1–2μm) along with fine scale Pb dispersoid at triple junctions or at the grain boundaries of Cu. Importantly, a high hardness of around 2.2GPa and relative density of close to 90% relative density (ρtheo) have been achieved for Cu–15wt% TiB2–10wt% Pb composite. Such property combination has never been reported for any Cu-based nanocomposite, by conventional processing route. In reference to the tribological performance, fretting wear tests were conducted on the sintered nanocomposites and a good combination of steady state COF (0.6–0.7) and wear rate (10–4mm3/Nm) were measured. An inverse relationship between wear rate and hardness was recorded and this commensurates well with Archard’s relationship of abrasive wear. The formation of a wear–resistant delaminated tribolayer consisting of TiB2 particles and ultrafine oxide debris, (Cu, Fe, Ti)xOy as confirmed from subsurface imaging using focused ion beam microscopy has been identified as the key factors for the low wear rate of these composites.

Effects of Sr on the microstructure and mechanical properties of in situ TiB2 reinforced A356 composite

In situ A356–3wt.% TiB2 composites were fabricated via a remelting and diluting (RD) approach, to investigate the effect of Sr on the modification of in situ A356–TiB2 composites with respect to the composite prepared by the conventional flux assisted synthesis (FAS) approach. The tensile properties of the composites were tested to evaluate the modification efficiency of Sr in different approaches. The results demonstrated that the RD composite can achieve fully modified eutectic structures than the FAS one owing to avoidance of the Sr–B interaction, which is commonly encountered in the FAS composites. The addition of Sr greatly improves the mechanical properties (especially the elongation) of thus prepared composites, only when the composites are in a fully modified state. Optimum modification of in situ A356–3wt.% TiB2 composite was obtained with Sr addition in the range around 0.03wt.%. The elongation of the 0.03wt.% Sr modified RD A356–3wt.% TiB2 composite are 6.6% and 5.6%, in as-cast and T6 states, respectively. The improvements in strength and ductility are attributed to the morphology change of Si as well as the improved melt cleanliness.

Effect of graphite addition on mechanical behavior of Al6061/TiB2 hybrid composite using acoustic emission

The present work includes the effect of addition of graphite for improving the properties of Al6061–TiB2 composite using the high-energy stir casting method. The characterization was performed with X-ray diffraction, energy dispersive spectrum and scanning electron microscope. The thermal and mechanical behaviors such as thermo gravimetric analysis/differential thermal analysis, hardness, tensile strength using acoustic emission and fatigue behaviors were investigated. The composite of composition Al6061–20% TiB2 with 2% graphite shows the greatest improvement in mechanical behavior. An Acoustic Emission system was employed in all the tests to monitor the acoustic energy release during the whole deformation process and some useful conclusions were drawn.

Comparative study of microstructures and mechanical properties of in situ Ti–TiB composites produced by selective laser melting, powder metallurgy, and casting technologies

Abstract

Densification and mechanical properties of cBN–TiN–TiB2 composites prepared by spark plasma sintering of SiO2-coated cBN powder

Abstract cBN–TiN–TiB 2 composites were fabricated by spark plasma sintering at 1773–1973 K using cubic boron nitride (cBN) and SiO 2 -coated cBN (cBN(SiO 2 )) powders. The effect of SiO 2 coating, cBN content and sintering temperature on the phase composition, densification and mechanical properties of the composites was investigated. SiO 2 coating on cBN powder retarded the phase transformation of cBN in the composites up to 1873 K and facilitated viscous sintering that promoted the densification of the composites. Sintering at 1873 K, without the SiO 2 coating, caused the relative density and Vickers hardness of the composite to linearly decrease from 96.2% to 79.8% and from 25.3 to 4.4 GPa, respectively, whereas the cBN(SiO 2 )–TiN–TiB 2 composites maintained high relative density (91.0–96.2%) and Vickers hardness (17.9–21.0 GPa) up to 50 vol% cBN. The cBN(SiO 2 )–TiN–TiB 2 composites had high thermal conductivity (60 W m −1 K −1 at room temperature) comparable to the TiN–TiB 2 binary composite.

Development of TiB2 reinforced aluminum foundry alloy based in situ composites – Part II: Enhancing the practical aluminum foundry alloys using the improved Al–5 wt%TiB2 master composite upon dilution

This is Part II of the two part study. Part I we dedicated to optimization of the fabrication of in situ TiB2 particulate reinforced aluminum matrix composites. In this part, efforts were made to confirm the strengthening effects of the Al–5wt% TiB2 composite, as a “master composite”, on the practical foundry alloys, i.e. AlSi7Mg0.3, AlCu4.5Si1.1 and AlZn6Mg0.5. Experimental work and theoretical analysis are presented to interpret the improved yield strength of the diluted composites as influenced by their microstructures. The theoretically predicted and fitted values were in good agreement with the observed microstructural features and particle distribution, strongly supporting the mechanisms we proposed. The remelting and diluting approach can achieve superior improvement in UTS with respect to the conventional halide salt route, while compromising less ductility of the final composite. This characteristic is attractive from both technological and economic standpoints. Technologically, the present work can assist in providing strengthening strategies for different aluminum foundry alloy systems.

Mechanical behavior and wear prediction of stir cast Al–TiB2 composites using response surface methodology

Al6061 was reinforced with various percentages of TiB2 particles by using high energy stir casting method. The characterization was performed through X-ray Diffraction, Energy Dispersive Spectrum and Scanning Electron Microscope. The mechanical behaviors such as hardness, tensile strength and tribological behavior were investigated. Wear experiments were conducted by using a pin-on-disc wear tester at varying load. The curve fitting technique was used to develop the respective polynomial and power law equations. The wear mechanism of the specimen was studied through SEM. Response Surface Methodology was used to minimize the number of experimental conditions and develop the mathematical models between the key process parameters namely weight percentage of TiB2, load and sliding distance. Analysis of Variance technique was applied to check the validity of the developed model. The mathematical model developed for the specific wear rate was predicted at 99.5% confidence level and some useful conclusions were made.

Comparative Study of Composites Reinforced With SiC and TiB2

In this present work an effort has been made to fabricate and compare the properties of aluminium metal matrix composites. Two specimens were fabricated by adding 10wt % of SiC and TiB2 with aluminium metal matrix. The two specimens were fabricated using stir casting route with bottom pouring technique. Morphology of the cast composites reinforced with SiC 10wt % and TiB2 10wt % were studied in detail by optical microscopy to analyze particle distribution in the aluminium metal phase. The hardness test was carried out to find out the hardness of the cast composites using Vickers hardness testing machine. The hardness test and its comparison show that the hardness value of SiC composite is higher than TiB2 composite. Mechanical testing was carried out on the tensile samples prepared from the two cast composite specimens. From tensile test results it has been observed that the tensile strength of TiB2 composite is 30% higher than SiC composite. Wear test was carried out to study the wear resistance behavior of cast composites. Wear test analysis proves that the wear resistance behavior of TiB2 composite is higher than SiC composite.

Preparation and scratch test of AlMgB14 modified by TiB2

In this paper, the AlMgB14 and AlMgB14–TiB2 composites were synthesized by means of mechanical alloying and the field-activated and pressure-assisted synthesis process. The effect of temperature and pressure on the purity and property of products was discussed. The results show that the process of preparing AlMgB14 bulk materials is optimized as follows: synthesis temperature 1,400–1,500 °C, heating rate 100 °C·min−1, axial pressure 60 MPa, heat preservation 8–10 min, optimum starting powders’ ratio Al: Mg: B = 0.1915:0.1363:0.6722, and adding excessive 3 wt% Al. The abrasion resistance of AlMgB14 composites with varying amounts of TiB2 was studied using single-point diamond scratch tests with loads ranging from 10 to 100 N in 10 N increments. The scratch width increases almost linearly with the applied load and decreases with TiB2 proportion increasing up to 70 wt%. With its advantages of fast heating, short reaction time, energy conservation, and high purity, this method offers a new way to synthesize AlMgB14 and AlMgB14–TiB2 composites.

Effect of high magnesium content on microstructure of Al–7Si alloy

A new class of ternary Al–7Si–xMg alloys was developed with improved microstructure consisting of fine spheroidal Mg2Si and eutectic Si particles dispersed in α-Al. The studies show that Mg and Sr have a modification effect on eutectic Si and Mg2Si particles respectively. In alloys with high Mg, a combination of Sr addition followed by T6 treatment resulted in a fine and spheroidal eutectic mixture of Si and Mg2Si. It was concluded that 2wt% Mg is optimum to obtain a minimum amount of coarse Mg2Si particles in the Al–7Si–xMg system as well as modify the eutectic Si particles. Furthermore, the hardness of Al–7Si–xMg alloys with and without Sr addition is comparable with those of in-situ Al–7Si–TiB2 composites indicating that they can be used as an alternative for the composites for wear resistant applications.

Spark plasma sintering of TiN–TiB2 composites

TiN–TiB2 composites were fabricated by spark plasma sintering at 1773–2573 K. Effects of TiN and TiB2 content on relative density, microstructure, and mechanical properties were investigated. Above 2373 K, TiN–TiB2 composites exhibited relative densities over 95%. A high density of 99.7% was obtained at 2573 K with 20–30 vol% TiB2. Shrinkage of the TiN–70 vol% TiB2 composite was the highest at 1573–2473 K. For the TiN–70 vol% TiB2 composite prepared at 1973–2373 K, TiN grains were small, while at 2573 K, TiB2 became a continuous matrix, in which irregular-shaped TiN dispersed. hBN was formed in the TiN–TiB2 composite containing 50–60 vol% TiB2 above 2373 K. The maximum Vickers hardness and fracture toughness obtained for the TiN–80 vol% TiB2 composite sintered at 2473 K was 26.3 GPa and 4.5 MPa m1/2, respectively.

Reaction mechanism, microstructure and properties of Ti–TiB insitu composite processed by spark plasma sintering

Conventionally, Ti–TiB composites have been processed using TiB2 or elemental boron in titanium. We report a novel method of processing Ti–TiB composite insitu through reaction between an inexpensive precursor, KBF4, and Ti using spark plasma sintering (SPS). The reaction mechanism was evaluated by differential scanning calorimetry (DSC) in combination with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The reaction happens in steps that involve different intermediate phases which finally lead to TiB. No residual TiB2 was found in the final composite unlike other methods. The insitu formed TiB whiskers refined the grain size and also homogenized the microstructure. The hardness and compressive strength increased significantly compared to cp Ti processed under same conditions.