Development of Al 6063–TiB2 in situ composites

In situ TiB₂ reinforced Al 6063 composites have been successfully synthesized through the chemical reaction between Al–10%Ti and Al–3%B master alloys in the Al 6063 alloy using liquid metallurgy route. The amount of TiB₂ formed in the composite is estimated using gravimetric analysis. Mechanical properties in terms of microhardness, ultimate tensile strength and modulus of elasticity have been improved by 21%, 47% and 65% respectively in comparison with matrix alloy. Further, ductility in terms of percentage elongation of the composites was found to increase by about 368% when compared with the matrix alloy. The improvement in ductility may be associated with the grain refinement of the composite with an increase in the content of Al–3%B master alloy.     

Microstructural evolution in ultrasonically processed in situ AZ91 matrix composites and their mechanical and wear behavior

AZ91 alloy matrix composites reinforced with phases formed in situ from the addition of Si particles were fabricated by solidification under ultrasonic vibrations. Application of high-intensity ultrasonic field to the melt resulted in optimized size, morphology and distribution of in situ formed Mg₂Si particles. The amount of Mg₂Si particles increased, its size was refined and the distribution became uniform. Heterogeneous nucleation from the addition of silicon particles and enhanced nucleation from rapid cooling refined the grain size of the matrix in the composites. Hardness and ultimate compressive strength of the composites increased as compared to that of the cast AZ91 alloy. Composites exhibited improved sliding wear behavior of under varying normal loads. Identified dominant wear mechanism at lower sliding velocities is abrasion. Improvement in mechanical and sliding wear properties of the composites is attributed to the refinement of both matrix and reinforcement phases and improved dispersion of the reinforcement under ultrasonic vibrations.     

Dry sliding wear of TiB2 particle reinforced aluminium alloy composites

Abstract

Al–4 wt-%Cu alloy and composites reinforced with 10 and 20 vol.-% of TiB₂ particles were prepared by powder metallurgy followed by hot isostatic pressing. The dry sliding wear behaviour of specimens of these materials was investigated. Pin-on-disc measurements showed that the wear resistance of Al–4Cu alloy can be improved dramatically by the addition of 20 vol.-%TiB₂ particles. This was due to the high hardness of the TiB₂ particles, and to strong particle–matrix bonding. The wear data were found to correlate with SEM observations.     

Sliding wear behaviour of Al 6063/TiB2 in situ composites at elevated temperatures

A low cost system of Al 6063 ? xTiB₂ (x = 0, 5, 10 wt.%) in situ metal matrix composites (MMCs) were prepared by the reaction mixture of K₂TiF₆ and KBF₄ with molten alloy. These in situ prepared composites were characterized by using scanning electron microscope, X-ray diffractometer, and microhardness analysis. The dry sliding wear behaviour of the prepared composite was investigated by using a Pin on Disc method at different applied loads of 9.8, 19.6 and 29.4 N for various temperatures (100, 200 and 300 °C). The study at room temperature was also carried out for comparison purpose. The results indicate that the wear rate decreases with the increase in the weight percentage of TiB₂, while it increases with the increase in the applied load.     

Dry sliding wear behaviour of AA 6351-ZrB2 in situ composite at room temperature

In the present work, AA 6351-xZrB₂ [x = 0, 3, 6 and 9 weight percentage (wt.%)] in situ composites have been prepared by the reaction of mixture of K₂ZrF₆ and KBF₄ with molten aluminium alloy at a reaction temperature of 850 °C. The in situ prepared composites were characterized by using scanning electron microscope (SEM), X-ray diffractometer (XRD), and microhardness analysis. The sliding wear properties of the prepared composite at room temperature were estimated by a pin-on-disc wear testing equipment using the composite material; the pins were machined according to standard sizes, and the tests were conducted as per the standards recommended by the ASTM G99-95a designation of different weighing percentage at room temperature. The wear characteristics of the composite in the as-cast, the solutionized and the solutionized-aged conditions were studied by conducting sliding wear test at the load of 9.81 N. The results indicated that the wear rate was decreased with an increase in the weight percentage of ZrB₂ and the wear resistance was increased with an increase in the fraction of ZrB₂ particulates in composite before and after heat treatment.     

Electroforming of TiB2-Reinforced Copper Matrix Electrode for EDM

TiB₂ particle-reinforced copper matrix composite is electroformed in copper sulfate on stainless steel plate. The impact of the particle content in electroforming solution on the surface morphology, hardness, and electrical conductivity of the electroformed composite are studied, and the influence of electroforming current density on the effective content of particles in the composite is also analyzed. The results show that when the content of particles in electroforming solution is 25 g/L, the current density is 4 A/dm², particles in the electroformed composite are well-distributed, and the average grain diameter can be reduced to 20 µm. The microhardness of Cu/TiB₂ composite reinforced by particles with diameter of 3 µm is 25% higher than that of electroformed copper, and its conductivity remains 86% of the copper.     

Fabrication of (TiB<Subscript>2</Subscript> − TiC)<Subscript>p</Subscript>/AZ91 magnesium matrix hybrid composite

Magnesium MMCs reinforced with TiB₂−TiC particulates were fabricated successfully via a master alloy route using a low cost Al-Ti-B₄C system as starting material system. Microstructural characterization of the (TiB₂−TiC)/AZ91 composite shows relatively uniform distribution of TiB₂ and TiC particulates in the matrix material. Moreover, the results show that the hardness and wear resistance of the composites are higher than those of the unreinforced AZ91 alloy.     

Microstructural characterisation and thermal stability of in situ TiB2/60Si–Al composite synthesised by displacement reactions and spray forming

Abstract

A novel in situ reactive technique has been employed for preparing 2·0 wt-%TiB₂/60Si–Al composite. The kinetic equations and the Arrhenius type equation were applied to compute the coarsening rate constant and the activation energy for grain growth for the composite when it was heated at semisolid state for partial remelting. Experimental results have shown that the in situ TiB₂ particles can refine effectively the primary Si phase and restrain the Si phase growth. The cubic coarsening rate constant for the composite was computed to be in the range of 75–148 μm³ min^?1 at temperatures in the range of 600–700°C, which was much less than that for the 60Si–Al alloy (1323–4523 μm³ min^?1). The value of activation energy for grain growth for the composite was about twice of that for the 60Si–Al alloy. The composite exhibited a higher thermal stability than that of the 60Si–Al alloy, suggesting that the in situ TiB₂ particles can effectively pin the grain boundaries and arrest the migration of liquid film in the semisolid state of the composite.     

Microstructural Analysis of the Reinforced Al‐Cu5mgti/Tib2 5 wt % Alloy for Investment Casting Applications

The paper describes the influence of 5 wt % titanium diboride (TiB₂) particles on the microstructure of an Al‐Cu alloy produced by plaster casting process. The elaboration route leads to a composite material with 1% of in situ TiB₂ particles and 4% ex situ of TiB₂ particles. The comparison of the reinforced alloy with the corresponding non‐reinforced counterpart makes clear that the presence of TiB₂ particles has a large influence in the observed microstructure. The presence of TiB₂ particles decreases the grain sizes and the porosity level. It is also found that TiB₂ particles play an important role in the precipitation events of Al₂Cu precipitates that are formed during solidification at the TiB₂/aluminum matrix interfaces.     

(Mg2B2O5w+ND)/ZK60镁基复合材料的摩擦磨损性能研究

在湿球磨条件下以600 r/min高能球磨混粉,并将球磨后的粉末经过热压烧结-热挤压成型制备(Mg2B2O5w+ND)/ZK60镁基复合材料。研究了(Mg2B2O5w+ND)/ZK60镁基复合材料在不同载荷和转速下的干摩擦磨损性能。结果表明:干摩擦条件下,材料的摩擦系数随着滑动距离的增加会经历跑和阶段和稳定阶段;材料的质量磨损率随着转速的增大而降低,随着载荷的增大而增大,且基体镁合金的质量磨损率始终低于复合材料。随着摩擦载荷和转速的增加,材料的摩擦系数减小,然后逐渐趋于平稳。混杂增强的镁基复合材料相比基体合金具有更低的摩擦系数。     

Tribological behaviour of hot extruded Al–Cu–Mg–Ag alloy reinforced by TiB2 particles

In the present investigation, tribological behaviour of the hot extruded Al–Cu–Mg–Ag (matrix) alloy and the effect of Ti and TiB₂ addition in matrix alloy have been studied. Hot extrusion was introduced to eliminate cast defects like porosity, voids and micro cracks. Addition of Ti and TiB₂ particles increased the hardness of the matrix by grain refinement and dispersion hardening, respectively. It has been observed that the increase in hardness had significantly improved the wear resistance of the material. Detail study of the wear surfaces and debris were carried out to understand the wear mechanism of the samples. It revealed a complex mechanism of micro-cutting, plastic deformation, abrasion and delamination of the wear samples.     

The relationship between TiB<Subscript>2</Subscript> volume fraction and fatigue crack growth behavior in the in situ TiB<Subscript>2</Subscript>/A356 composites

The relationship between TiB₂ volume fraction and fatigue crack growth behavior in the A356 alloy matrix composites reinforced with 3, 5.6, and 7.8 vol% in situ TiB₂ particles has been investigated. The mechanisms of crack propagation in the TiB₂/A356 composites were also discussed. The results show that the 3 vol% TiB₂/A356 composite has nearly the same crack growth behavior as the matrix alloy, while the 5.6 vol% TiB₂/A356 composite exhibits a little bit faster crack growth rate. The 7.8 vol% TiB₂/A356 composite presents the lowest resistance to crack growth, indicating that the crack growth is accelerated by increasing TiB₂ volume fraction. Fractographies reveal that an increase in TiB₂ volume fraction results in a change from the formation of striation and slip to the failure of voids nucleation, growth, and coalescence. Cracks tend to propagate within the matrix and avoid eutectic silicon and TiB₂ particles in the intermediate ΔK region, while prefer to propagate along interfaces of eutectic silicon and TiB₂ particles and link the fractured eutectic silicon particles in the near fractured ΔK region. Furthermore, the propensity for the separation of TiB₂ increases with the increase in TiB₂ volume fraction. The massive voids caused by fractured eutectic silicon and separated TiB₂ particles propagate and coalesce, and then accelerates the crack growth in TiB₂/A356 composites.     

Surface modification of titanium alloy with laser cladding RE oxides reinforced Ti3Al–matrix composites

Ti₃Al–matrix composites were prepared by laser cladding of the Al₃Ti/TiB₂/Al₂O₃ pre-placed powders on the Ti–6Al–4V alloy, which can improve the wear resistance of the substrate. With addition of the proper content of RE oxides (nano-Y₂O₃), this composite coating exhibited finer microstructure and better wear resistance. Nevertheless, excessive RE oxides could lead to the production of the micro-crack, and also decrease the temperature of the molten pool leading to the present of the un-melted TiB₂ block, which can significantly decrease the wear resistance of this composite coating.     

Wear and corrosion studies of graphite‐aluminum composite reinforced with micro/nano‐TiB2 via spark plasma sintering

The demand for lightweight materials in the automobile and aerospace industries has led to various researches on graphite and graphite‐aluminum composites. The aim of this study was to investigate the effect of the addition of micron/nano TiB₂ particles on the properties of graphite‐aluminum composite particularly the wear resistance. The powders were sintered at 550 °C and 50 MPa with more attention on the effect of the sintering temperature on densification, microhardness, coefficient of thermal expansion, wear and frictional force. The results show that the addition of nano TiB₂ reduces the densification while improving the hardness of Gr?Al composite with the lowest value being 96.0 % of relative density and the highest microhardness of 43.58 HV 0.1. The coefficient of thermal expansion and frictional force of the composite materials increases with increasing TiB₂ content and heating rate (100 °C/min–150 °C/min). TiB₂ particles enhance the wear resistance of graphite‐aluminum composite. The addition of micro/nanoparticles of TiB₂ to graphite‐aluminum composite increases its corrosion rate with improved passivation behavior in 3.5 wt.% NaCl solution. Nevertheless, 5 wt.% nano (100 °C/min) TiB₂ additions do not affect the overall corrosion rate. This work has shown that we can take advantage of some of the properties of TiB₂ to improve the performance of graphite‐aluminum composite.     

Fabrication of Co-Based Coatings on Titanium Alloy by Laser Cladding with CeO2 Addition

In this study, Co-based laser cladding coatings reinforced by multiple phases were fabricated on titanium alloy. Co42 Co-based self-fluxing alloy, B₄C, and CeO₂ mixed powders were used as the precursor materials. The coatings were mainly composed of γ-Co/Ni, CoTi₂, CoTi, NiTi, TiC, Cr₇C₃, TiB₂, and TiB phases. A typical TiB₂/Cr₇C₃/TiC composite structure was chosen. It was found that CeO₂ did not influence the phase types of the coating significantly, but was effective in refining the microstructure and enhancing the microhardness and dry sliding wear resistance. Compared with the Ti-6Al-4V titanium alloy, the microhardness and wear resistance of the composite coatings were enhanced by 3.44–4.21 times and 14.26–16.87 times, respectively.     

Effects of Al2O3 particle reinforcement on the lubricated sliding wear behavior of ZA-27 alloy composites

The present investigation deals with the effect of Al₂O₃ particle reinforcement on the lubricated sliding behavior of ZA-27 alloy. The composites with 3, 5, and 10 wt% of Al₂O₃ particles were produced by the compocasting procedure. Tribological properties of alloy and composites were studied, using block-on-disk tribometer at different specific loads and sliding speeds. The test results revealed that composite specimens exhibited significantly lower wear rate, but higher coefficient of friction than the matrix alloy specimens in all the combinations of applied loads and sliding speeds. The improved antiwear characteristics of the composites were influenced by positive effects of higher frictional heating on compatibility of the composite phases and suppressing micro-cracking tendency. Due to that, effects of reinforcing hard particles were manifested through the reduced wear rate of composites, especially in conditions of higher load, lower sliding speeds and higher Al₂O₃ particle content. In present wear tests, the significant forming of mechanically mixed layers was not noticed, what is confirmed by the SEM microphotographs.     

Study on squeeze casting of an in situ 5 vol.-% TiB2/2014 Al composite

Abstract

An in situ 5 vol.-% TiB₂/2014 composite was prepared by an exothermic reaction of K₂TiF₆, KBF₄ and Al melts. The effect of introduction of in situ formed TiB₂ particles on the squeeze-casting formability of the composite was discussed. The microstructural evolution and changes in the mechanical properties of the composite at different squeeze pressures were investigated. The results showed that a pouring temperature of 710°C, a die temperature of 200°C and a squeeze pressure of 90 MPa were found to be sufficient to get the qualified squeeze cast and maximum mechanical properties for an Al 2014 alloy. However, the pouring temperature, die temperature and squeeze pressure need to be increased to 780°C, 250°C and 120 MPa for the composite to get the qualified squeeze cast and maximum mechanical properties as a result of the effect of introduction of in situ formed TiB₂ particles on the solidification process, plasticity and fluidity of the composite. The microstructural refinement, elimination of casting defects such as shrinkage porosities and gas porosities and improved distribution of TiB₂ particles in the case of the composite result when pressure was applied during solidification. Compared with the gravity-cast composite, the tensile strength, yield strength and elongation of the squeeze-cast composite at 120 MPa increased by 21%, 16% and 200%.     

The relationship among microstructure evolution,mechanical property and in situ reaction mechanisms in preparing Cu–1.6wt%TiB2 alloys

The Cu–1.6wt%TiB₂ alloys have been prepared by combining mechanical alloying and heat treatment. The relationship among microstructure evolution, mechanical property and in situ reaction mechanisms in synthesizing Cu–1.6wt%TiB₂ alloys was investigated. It is shown that the temperature 750 °C measured by DSC can cause the occurrence of in situ reaction between B and Ti elements in the Cu–B–Ti alloy powders ball milled for 40 or 60 h; An upward trend of the hardness appears after heat treatment at 700 °C, and the highest value reaching 335HV, but a downward trend appears after heat treatment at either 500 °C or 900 °C; Many coarse B particles were formed in the copper matrix after heat treatment at 500 °C, the number and size of the formed B particles significantly increases with increasing time, but many reaction boundaries (or TiB₂ films) and finer TiB₂ particles can be formed after heat treatment at both 700 °C and 900 °C. The different in situ reaction models between Cu–B and Cu–Ti alloy micelles with different distribution levels were established and analyzed.     

Experimental investigation on mechanical properties and wear characterization of Al-Si12CulMg1 aluminium alloy reinforced with titanium diboride and boron carbide particulate hybrid composites using stir casting process

LM13 aluminium alloy (Al−Si12CulMg1) with titanium diboride (TiB₂) and boron carbide (B₄C) particulate hybrid composites have been prepared using stir casting process. Wt% of titanium diboride is varied from 0–10 and constant 5 wt% boron carbide particles have been used to reinforce LM13 aluminium alloy. Microstructure of the composites has been investigated and mechanical properties viz., hardness, the tensile strength of composites have been analyzed. Wear behavior of samples has been tested using a pin on disc apparatus under varying load (20 N–50 N) for a sliding distance of 2000 m. Fracture and wear on the surface of samples have been investigated. Microstructures of composites show uniform dispersion of particles in LM13 aluminium alloy. Hardness and tensile strength of composites increased with increasing wt % of reinforcements. Dry sliding wear test results reveal that weight loss of composites increased with increasing load and sliding distance. Fracture on the surface of composites reveals that the initiation of crack is at the interface of the matrix and reinforcement whereas dimples are observed for LM13 aluminium alloy. Worn surface of composites shows fine grooves and delamination is observed for the matrix.     

In situ TiB2 particulate reinforced near eutectic Al–Si alloy composites

In situ TiB₂ particulate reinforced near eutectic Al–Si alloy composites fabricated by the melt reaction composing (MRC) methods have been investigated. It has been shown that minute TiB₂ particles (less than 1 μm) uniformly distribute in the eutectic structure and they are interlaced with the coralline-like eutectic Si, while there are very few TiB₂ particles in α-Al. It has been also shown that in situ TiB₂ particles can enhance the tensile strength of the Al–Si alloy matrix. The strengthening effect increases with increasing TiB₂ content. The ultimate tensile strength (UTS) at room temperature of as-cast 6%TiB₂/Al–Si–Mg composite is 296 MPa, that is a 14.7% increase over the matrix, and its elongation at fracture is 5.5%. After heat-treatment (T6), the UTS of the composites reaches 384 MPa. The strengthening mechanism has been discussed.