Dispersion Of TiB2 Particles Research Articles

The effects of stress ultrasonic rolling on the surface integrity and fatigue properties of TiB2/7050 Al composite

In the present work, a new surface mechanical strengthening (SMS) technique named stress ultrasonic rolling (SUR), which is ultrasonic rolling (UR) assisted with a uniaxial tensile elastic stress field, was reported and successfully conducted on 5 % wt TiB2/7050Al composite. Based on the experimental analysis and numerical simulation, the effects of SUR on surface integrity and fatigue performance of the composite were comprehensively investigated. Compared with ordinary UR, SUR further enhanced the fatigue strength at 106 cycles of the composite by 5 % and prolonged the fatigue life of the composite under the stress level of 532.8 MPa by 1.8 to 3.3 times, which are attributed to the comprehensive effect of excellent surface finish, larger and deeper compressive residual stress (RSc) layer, dispersed TiB2 particles distribution in the surface, and superficial nanocrystalline structures. Besides, the assistance of uniaxial tensile elastic stress field did not increase the amount of surface plastic deformation, which indicates the RSc generated by SUR should have similar mechanical and thermal stability to that produced by ordinary UR treatment.

Agglomerating behavior of in-situ TiB2 particles and strength-ductility synergetic improvement of in-situ TiB2p/7075Al composites through ultrasound vibration

Agglomerates of in-situ particles are the key detrimental defects in particulate reinforced aluminum matrix composites (PRAMCs) by acting as Achilles' heel leading to the premature failure of the materials. Effective methods to disperse/eliminate these agglomerates rely on in-depth understanding of the agglomeration mechanism of the in-situ particles. In this work, the agglomerating behavior of TiB2 particles in Al-Ti-B system was investigated through the thermit reactions between mixed fluorides and molten aluminum. The results indicate that the morphological patterns of TiB2 agglomerates are inherited from the preformed Al3Ti intermedium. The formation of flocculent, shell and flaky TiB2 agglomerates are the results of the diffusing boron atoms continuously reacting with Al3Ti. The in-situ Al-TiB2 was used as a precursor to prepare TiB2p/7075 Al composites. In particular, ultrasound vibration treatment was applied to explore if a locally forced oscillation can deagglomerate the TiB2 agglomerates. Microstructural observations strongly support such speculation. Thanks to the deagglomeration and dispersion of TiB2 particles, both the strength and ductility of the PRAMC have been improved drastically. The fracture surface of the composites was transformed from particle debonding to the dominance of ductile fracture.

Achieving Superior Corrosion Resistance of TiB2 Reinforced Al-Zn-Mg-Cu Composites via Optimizing Particle Distribution and Anodic Oxidation Time

In this study, the effects of particle distribution and anodizing time on the microstructure and corrosion resistance of the TiB2 particle-reinforced Al-Zn-Mg-Cu composite were investigated. Relationships between TiB2 particle distribution, anodizing time, coating growth rule, and corrosion resistance were characterized and discussed using an optical microscope, a scanning electron microscope, an electrochemical test, and a salt spray test. Dispersion of TiB2 particles by powder metallurgy improved the corrosion resistance of the anodized coating on composites. Compared with the matrix, the corrosion potential (Ecorr) of the anodized coating shifted to the positive direction, and the corrosion current density (icorr) decreased. Meanwhile, the icorr of the coating decreased initially and then increased with the extension of the anodization time. The corrosion resistance of the coating was optimal at an anodization time of 20 min. The corrosion resistance of the composite was determined by both the porosity and thickness of the coating. Additionally, all samples treated by potassium dichromate sealing had no corrosion points after a 336-h salt spray test, demonstrating an excellent corrosion resistance suitable for harsh environmental applications in industry.

Study of steel matrix composite samples with 12%Wt TiB2 produced by spark plasma sintering

Composites consisting of a steel matrix reinforced with diluted ceramics have been investigated as a way to reduce weight and increase wear resistance. This paper describes a composite made with TiB2 ceramic powder and a microalloyed steel turned into powder by the top-down technique. The dispersion method of 12% weight percentage of TiB2 particles in the steel powder was performed by cryomilling techniques. With this powder, bulk TiB2 steel/ceramic samples were produced using the Spark Plasma Sintering (SPS) process. The produced steel matrix composite samples with 12%wt TiB2 were characterized and showed a low level of porosity. The multiphysics fields associated with the SPS process activated the recovery mechanisms that formed a nanostructure in the ferritic matrix. The dispersion of TiB2 particles in microalloyed caused a reduction in abrasive wear of 36.8% as compared with low alloy steel used. This reduction was accompanied by a 5% reduction in density.

Structural-functional integrated TiB2/Al–Mg-Gd composite with efficient neutron shielding phases and superior mechanical properties

The structural-functional integrated TiB2/Al–Mg-Gd composite was fabricated by the powder metallurgy-based methods, including atomized composite powder fabrication, spark plasma sintering and hot extrusion techniques. In this manner, the atomization process effectively refined Gd-contained phases and dispersed TiB2 particles in composite powders. Such refinement was inherited to the as-extruded composite. In detail, the finer Gd-contained phase was confirmed to be τ(MgNi2-type) Laves phase. Functionally, the composite had high thermal neutron shielding efficiency (99%), which was higher than the published results for neutron shielding materials. This phenomenon was analyzed by the Shmakov-Yamamoto model. The theoretical simulation showed that the refinement of τ phases played a key role in improving the neutron shielding property, which agreed well with experiment results. Structurally, the yield strength, tensile strength and elongation of the TiB2/Al–Mg-Gd composite were 353 ± 5 MPa, 464 ± 6 MPa and 15.6 ± 0.4%, respectively. Such mechanical properties were considerably higher over available neutron shielding materials. Regarding the improved yield strength, both solution strengthening effect and grain refinement strengthening effect were quantitatively analyzed to be the major strengthen contributors. Finally, this novel composite can be a promising candidate for neutron shielding materials in future.

Structural evolution and mechanical properties of TiB2 reinforced 2024Al composite stimulated by heat treatment

The microstructural evolution and mechanical properties of 3 wt% TiB2p reinforced 2024Al (TiB2p/2024Al) composite stimulated by T6 heat treatment are reported in this work. Morphological results showed that the initial TiB2p/2024Al composite fabricated by laser-directed energy deposition (LDED) consists of fine equiaxed grains with well dispersed TiB2 particles, in which nanoscale Al2Cu(Mg) precipitates are dispersed in the Al matrix. After the T6 heat treatment, ultrafine Al2CuMg precipitates and few AlCuMnFe (T) dispersoids were observed in the matrix and grain boundaries. The sample which was solution treated at 495 °C temperature showed a higher compression yield strength of about 371.3 MPa and hardness of about 145HV, whilst the sample treated at 505 °C solution temperature (ST) had a relatively low compression yield strength of 289.8 MPa and hardness of about 128 HV. The reason is deduced to originate from the existence of negative factors such as the formation of microvoids. Quantitative analysis unveiled that grain refinement and Orowan strengthening should contribute to the high strength of the annealed TiB2p/2024Al composite.

Investigation on Inorganic Salts K2TiF6 and KBF4 to Develop Nanoparticles Based TiB2 Reinforcement Aluminium Composites.

In the current research, AA6082 aluminium alloy matrix composites (AAMCs) incorporated with various weight fractions of titanium diboride (0, 3, 6, and 9 wt%) were prepared via an in situ casting technique. The exothermic reaction between inorganic powders like dipotassium hexafluorotitanate (K2TiF6) and potassium tetrafluoroborate (KBF4) in molten Al metal contributes to the development of titanium diboride content. The manufactured AA6082-TiB2 AAMCs were evaluated using a scanning electron microscope (SEM) and X-ray diffraction (XRD). The mechanical properties and wear rate (WR) of the AAMCs were investigated. XRD guarantees the creation of TiB2 phases and proves the nonappearance of reaction products in the AMCs. SEM studies depict the even dispersion of TiB2 in the matrix alloy. The mechanical and tribological properties (MTP) of the AAMCs showed improvement by the dispersion of TiB2 particles. The WR decreases steadily with TiB2 and the least WR is seen at nine weight concentrations of TiB2/AA6082 AAMCs. Fabricated composites revealed 47.9% higher flexural strength and 14.2% superior compression strength than the base AA6082 alloy.

Study on the fabrication of in-situ TiB2/Al composite by electroslag melting

Abstract In-situ TiB2 particles can be synthesized via the salts-Al reaction by adding mixed K2TiF6 and KBF4 (Ti/B=1/2) salts into Al melt. In this research, a novel electroslag melting technology was proposed to synthesize TiB2 particles by the salts-Al reaction in order to reduce the reaction time period and purify the melt of composite. The effects of current of electroslag melting on the synthesis of TiB2 particles and mechanical properties of composite were investigated. The results showed that TiB2 particles could be in-situ synthesized by electroslag melting at 600 A for 15min. Compared with 60 min at 850°C of traditional LSM method, the efficiency of preparation was greatly improved. In addition, the dispersion of TiB2 particles in the composite prepared by electroslag melting was improved, meanwhile the non-metallic inclusions in the composite was reduced. The values of YS, UTS and El pct of composite prepared by electroslag melting were higher than that of the composite prepared by traditional LSM method.

Effect of electric current pulses on TiB2 particle dispersion in aluminum alloy melt

The effect of electric current pulses (ECPs) on the dispersion of TiB2 particles is investigated. The results demonstrate that Joule heating and the Peltier effect can reduce the binding force between TiB2 particles in the melt. The induced magnetic pressure, pinch force gradient and electromagnetic shock wave can disperse loose aggregations of TiB2 particles, thereby decreasing the size of the TiB2 particle clusters. The ECP parameters are found to have a large influence on the TiB2 particle cluster dispersion.

Study on the effect of CeO2 for fabricating in-situ TiB2/A356 composites with improved mechanical properties

In this paper, in-situ 5 wt% TiB2/A356 composites were fabricated via a salts-metal exothermic reaction process. The effects of CeO2 on the microstructures and mechanical properties of the composites at both as-cast and T6 conditions were investigated. The results showed that the addition of CeO2 could significantly improve the dispersion of TiB2 particles, refine the α-Al grains and modify the coarse lamellar eutectic Si into fine fibrous and granular structures. The optimum addition level for dispersion, refinement and modification was 0.5 wt% CeO2. The values of YS, UTS and El pct of the composite with 0.5% CeO2 in T6 condition were 259 MPa, 307 MPa and 6.4%, which were 14.1%, 8.7% and 39.1% higher than those of the composite without CeO2. The YS enhancement of composite with 0.5 wt% CeO2 was mainly due to the improvement in dispersion of TiB2 particles in the matrix. The improved elongation of composite with 0.5 wt% CeO2 was mainly attributed to the improvement in dispersion of TiB2 particles, the grain refinement, and the modification of eutectic Si phase.

Effects of Zn content on microstructures and mechanical properties of in-situ TiB2/Al-Zn-Mg-Cu composites subjected to hot extrusion

Microstructures and mechanical properties of in-situ TiB2 reinforced Al-xZn-2.5Mg-2.4Cu-0.15Zr composites with different Zn content (i.e. x = 6.9, 9 and 12 wt%) were studied in this work. Detailed microstructural investigations have been carried out via scanning electron microscopy and associated orientation imaging microscopy. The results indicate that as Zn content increased from 6.9 to 12 wt%, the severe clusters of TiB2 particles were noticeably dispersed owing to the decreased interfacial energy between TiB2 particles and Al matrix. The average grain size of extruded samples decreases and the grain shapes tend to be more equiaxed with the increase of Zn content, thanks to the formation of LAGBs and its transformation to HAGBs surrounding dispersed TiB2 particles in the grain. In addition, the yield strength of extruded samples increases from 597 MPa to 707 MPa with the increase of Zn content from 6.9 to 12 wt%, via grain-boundary strengthening mechanism and reinforcing particles strengthening mechanism.

Dispersion behavior of TiB2 particles in AISI D2 tool steel surfaces during pulsed laser dispersing and their influence on material properties

AISI D2 is one of the most applied cold-working tool steel for deep drawing operations, due to the materials good toughness and high wear resistance. However, since the lubricant-free deep drawing as well as the processing of high strength and ultra-high strength steel sheets remaining ongoing trends in the automotive industry, the tool surfaces need to be improved regarding their friction and wear behavior. For this purpose elevated micro textures can be applied. Since protruded micro features are predominantly affected by wear, a structuring process enabling the formation of suitable textures with high wear resistance is needed.In this paper surface texturing at microscale was conducted by laser implantation. This technique allows the fabrication of highly wear resistant, separated and elevated features (implants) on steel surfaces via a discontinuous dispersing of ceramic particles by pulsed laser radiation. The aim of this study was to investigate the techniques potential for the creation of wear resistant elevated micro features on AISI D2 tool steel surfaces by the application of TiB2 particles. The laser parameters (pulse power and length) were varied and a comparative material analysis on AISI D2 laser remelted spots and TiB2 localized dispersed zones was examined. High-speed camera recordings allowed the description of the particle insertion mechanism from pre-coatings during laser processing. Mechanical properties were analyzed by (micro-) hardness measurements at top and cross sections. The microstructure was investigated by optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The implants geometrical properties (diameter, height, depth) were investigated by white light interferometry and optical microscopy. The experiments reveal that a pulsed laser remelting of AISI D2 leads to a significant hardness drop due to high retained austenite (γR) contents. Contrary, a localized dispersing of TiB2 particles leads to defect free dome- or ring-shaped elevated features with hardness values up to 1800 HV1. The high hardness values result from the dispersed TiB2 particles and an in-situ precipitation of new hard particle phases, which lead to a reduction of the γR content within the matrix.

The preparation and mechanical properties of Al metal matrix composites by in-situ method

The aluminium-based composites are widely being used in the transport, aerospace, marine, automobile and mineral processing industries. Preparation of Al/TiB2 composites by in-situ processing offers significant advantages over the conventional processing from both technical and economic standpoints. The technique of salt-metal reactions is an attractive in-situ approach for preparing Al-TiB2 metal matrix composites. It involves in mixing of Ti and B bearing salts (i.e., K2TiF6 and KBF4) to molten aluminium, giving rise to the formation of dispersion of TiB2 particles in the aluminium matrix. The obtained as-cast metal matrix composite is carefully machined to prepare the test specimens for hardness, tensile as well as microstructure studies as per ASTM standards. The hardness, tensile strength and microstructure properties of Al6061-TiB2 composites are explored experimentally. Finally, the material characterisation of heat treated sample and as-cast samples are compared.

Microstructure of Multi-Pass Friction-Stir-Processed Al-Zn-Mg-Cu Alloys Reinforced by Nano-Sized TiB2 Particles and the Effect of T6 Heat Treatment

In this work, a fine-grained structure with a uniform distribution of TiB2 particles and precipitates was achieved in TiB2 particle-reinforced (PR) Al-Zn-Mg-Cu alloys by friction stir processing (FSP). The effects of multi-pass FSP on the microstructure, and TiB2 particle distribution, as well as the microstructural evolution in the following T6 treatment, were investigated by X-ray diffraction, scanning electron microscopy and associated electron backscattered diffraction. The results showed that the distribution of TiB2 particles and alloy precipitates was further improved with an increase in the FSP passes. Moreover, compared with alloy segregation in the as-cast PR alloys during T6 treatment, a complete solution of the precipitates was achieved in the FSP-treated PR alloys. The fine-grained structure of the FSP-treated PR alloys was thermally stable without any abnormal growth at the high temperature of T6 treatment due to the pinning effect of dispersed TiB2 particles. The strength and ductility of the PR alloys were simultaneously improved by the combination of FSP and T6 treatment.

Selective laser melting of TiB2/316L stainless steel composites: The roles of powder preparation and hot isostatic pressing post-treatment

Selective laser melting (SLM), a promising additive manufacturing technology, was used to fabricate TiB2/316L stainless steel composites. An important factor in manufacturing composites via SLM is feedstock powder preparation. In this work, the powders were prepared by either direct mixing or ball milling. The evolution of constituent phases, microstructural features, and size distribution with milling time was investigated. This research determined that powder particles were both coarsened and refined during the early stages of milling (0–6h), depending on the milling time. After 8h of milling, the powders exhibited a wide size distribution and stable spherical morphology, while the average crystallite size of the stainless steel matrix phase significantly decreased to 11.11nm due to severe plastic deformation. The powders obtained after 8h of mixing or milling were processed via SLM, and the microstructures exhibited a continuous ring-like structure of uniformly dispersed TiB2 particles. The hardness of the nanocomposite sample prepared from the ball milled powder exceeded that for samples made with the directly mixed powder, but only for those with the highest content of 15vol.% TiB2 reinforcement particles, due to finer particle sizes and enhancement of the wetting behavior in the molten pool. To increase the final density of these SLM-fabricated components with high hardnesses, a hot isostatic pressing (HIP) post-treatment was applied. The microstructural characteristics of the HIPed samples evolved with HIP holding time from equiaxed grains to segregated regions of coalesced reinforcement particles. In addition, significant drops in hardness and wear resistance values were observed after HIP treatment due to the high-temperature annealing effect.

Effect of Preparation Conditions of TiB<sub>2</sub> Particle Dispersed Al Composites on Microstructure

Pure aluminum (Al) has been used as high performance heat sink, electrical line and power supply line because of its light-weight, good thermal and electrical conductivities and high cost performance. On the other hand, the higher performance heat sink and eletrtorical line at room and high tempertture are reqired because of the increment of the power density and higher integration of semiconductor and LED. The use of Al matrix composites is one of suilable solution, because these parts needs multi functional propertes. In this study, titanium die-broide (TiB2) particles was selected as the dispersant in Al matrix composites because of its good thermal and electrical conductivity, and good mechanical propertes. At first, the mixed power of Al and TiB2 particles was obtained from six kinds of mixing process, which parameters are conventional boll milling, ultrasonic vibration after conventinal milling, planetary ball milling, which milling process was performed in wet process with ethanol and dry process. 20 vol. % TiB2/ Al composites was obtained from spark plasma sintering. The dence comopsites with over 98% in relative density with highly dispersed TiB2 particles was obtained from wet mixing process. But the tensile strength of the composites prepared from dry mixing process is higher than that of wet mixing process. The thermal conductivity of the composites is about 120 W/mK, and the obvious diferrence between the wet process and dry process was not observed.

CeO2 induced dispersive distribution of TiB2 particles in in situ TiB2/Al composite

The roles of CeO2 additive during preparation of in situ TiB2/Al composite, alleviating particle settlement in composite melt and significantly improving particle dispersion in final microstructure, are studied in this paper. It is evidenced that the CeO2 additive reacts with Al melts to release Ce solute into the melts, and the released surface active Ce is absorbed in the Al/TiB2 interfaces without any other reaction products. First principles calculations show that the interfacial energy of Al/TiB2 interfaces is reduced owing to the presence of Ce in Al/TiB2 interfacial area. Therefore, the wettability of molten Al on TiB2 surface is increased and the dispersion of TiB2 particles in Al matrix is eventually improved.

Behavior of CeO2 additive in in-situ TiB2 particles reinforced 2014 Al alloy composite

In-situ TiB2 particles reinforced 2014 aluminum alloy composite was prepared using an exothermic reaction process with K2TiF6 and KBF4 salts. The effects of CeO2 additive on the microstructure and properties of in-situ TiB2/2014 composite were investigated. The results showed that CeO2 at high temperature exhibits the same function as Ce. When 0.5% (mass fraction) CeO2 additive was added, the dispersion of TiB2 particles in the matrix is improved significantly, and particles have no obvious settlement. The dispersing mechanism of TiB2 particles in 2014 Al alloy matrix was explained. Compared with the composite without CeO2, the hardness, tensile strength, yield strength and elongation of the composite with CeO2 addition are greatly increased in as-cast condition.

<i>In Situ</i> TiB<sub>2</sub> Particles Reinforced Copper Matrix Composite Coating on Mould Steel by Laser Cladding

To extend the mould cycle duration and to reduce cost, a TiB2 particulate reinforced Cu based composite coating was produced on hot-working die steel substrate using laser cladding. The experimental results showed that TiB2 particles embedded in copper based alloy were in-situ synthesized during laser processing. An excellent bonding between the coating and the substrate was obtained. The microstructure of the coating was mainly composed of -Cu dendrites and dispersed TiB2 particles. The maximum microhardness of the coating was about 800HV0.2. The wear resistance of the coating was evaluated under room temperature dry-sliding wear test condition. Due to the presence of a large amount of TiB2 particles, the composite coating exhibited excellent wear resistance compared with that of substrate.

On the kinetics of diffusion controlled precipitation under microgravity

Metal matrix composites have many desirable characteristics for precision components, e.g., light weight, dimensional stability, and high thermal conductivity. The understanding of the mechanisms and processes taking place at their production is of crucial importance, since these factors are important for the properties of the composite and its future application. A theoretical model of the processes at diffusion controlled formation of TiB2 in liquid Al under microgravity has been proposed. The main features of the developed model are: mechanisms controlling the formation of the TiB2; degree of distribution of the dispersed TiB2 particles; and mean size and size distribution of the dispersed TiB2 particles. The results obtained with the aid of the proposed model were verified on our recent experiments at the STS95 space shuttle mission. The model predicts correctly the TiB2 particles distribution along the specimens and the characteristic split of the reaction zone observed experimentally.