Enhancement of hardness and wear strength of pure Cu and Cu–TiO₂ composites via a friction stir process while maintaining electrical resistivity

Kumar S., Malik N., Cinelli P., Sharma V.

Aluminum alloy based metal matrix composites are widely used in different engineering applications that are subjected to dynamic loading conditions. In the present study, aluminum alloy Al-Si7Cu3Mn0.5(LM27) composites are manufactured by a stir casting route with two different weight percentages and different size of SiC and TiO2. The reinforcement particles of 15 µm and 115 µm sizes are reinforced in a concentration of 3wt. % and 12wt. %. Split Hopkinson pressure bar is used to evaluate dynamic compressive behavior of the composites at the strain rate of 700, 1500 and 2500 s−1. Microstrucutral examination of fine size reinforced composites exhibited the formation of globular silicon that is arranged around the particles. Micro-hardness of the particle–matrix interface of the fine particle reinforced composite is higher in comparison to composite reinforced with coarse particles. At the strain rate of 700 s−1, at higher concentration of reinforcement particles the fine particles reinforced composites exhibit maximum strength whereas lower concentration of fine particle reinforced composite showed the maximum strain. Strain sensitivity is exhibited by all the composites and strength shows an increasing trend with an increase in the strain rate. The fine particles reinforced composites exhibited maximum flow stress at higher weight percent of reinforcement particles whereas maximum strain is found at lower weight percent of fine particles. The dynamic compressive behavior of composite is found dependent on the degradation of elastic modulus, stress localization phenomena and debonding characteristics.

Yaghoubi M.A., Anjabin N., Kim H.S.

Pure Cu sheets with severe plastic deformation were obtained using constrained groove pressing (CGP) and subjected to different passes of friction stir processing (FSP) with and without yttria nanoparticles. The fine grain structure of the CGP-treated samples underwent rapid grain growth during 1-pass FSP without nanoparticles. The addition of yttria particles resulted in a very fine-grained structure in the stir zone (SZ) with a high hardness value and the lowest weight loss during the wear test. Applying 3 passes of FSP resulted in homogeneous dispersion of reinforced particles in both the annealed and CGP processed samples. The SZ of the sample that was processed with CGP and 3-pass FSP in the presence of yttria had a finer grain with higher strength and wear resistance than the FSP-treated annealed samples.

Samal P., Tarai H., Meher A., Surekha B., Vundavilli P.R.

This study focuses on a comparative analysis of mechanical behavior and microstructural characteristics of Cu matrix (C87600) based hybrid composites reinforced with SiC-Grp and WC-Grp fabricated by the stir casting process. The graphite particle percentage was kept constant, whereas the content of SiC and WC in the respective composites was varied to analyze the mechanical properties of the fabricated composites. The morphological observation was carried out by field emission scanning electron microscope (FESEM), which revealed uniform dispersion of the reinforced particles in the hybrid composites. Clear phases of SiC and WC along with the Cu alloy were identified by the x-ray diffractometer (XRD). Further, a comparative study was conducted to analyze the mechanical behavior of the Cu-SiC-Gr and Cu-WC-Gr hybrid composites. With the addition of the hard ceramic materials, the tensile behavior and microhardness of both the Cu-based MMCs were improved. The WC-Gr reinforced composites exhibited higher mechanical properties than the SiC-Gr reinforced hybrid composites. Further, the fracture surfaces were also characterized to study the tensile behavior of the fabricated copper-based hybrid composites, which shows that ductile fracture was mainly associated with both hybrid composites.

Naik R.B., Reddy K.V., Reddy G.M., Arockia Kumar R.

In this work, pure copper and copper-tungsten (Cu-W) surface composite is produced using a single pass friction stir processing (FSP) with an intention to enhance the hardness and wear resistance without impairing electrical conductivity. FSP is performed by changing the traverse speed from 50 to 200 mm/min and at a constant tool rotational speed of 600 rpm. The samples extracted from the stir zone are characterized for their microstructure, hardness, wear behaviour and electrical conductivity. The average grain size, at the stir zones, was significantly reduced (from 40 to 3 µm) after FSP. In the case of pure copper, the grain size decreased from 9 to 3 µm with an increase in traverse speed, however, grain size increased from 4 to 6 µm in the case of Cu-W composite. The hardness of FSP’ed Cu and FSP’ed Cu-W surface composite was increased in the order of 52% and 130% compared to the unprocessed copper. The wear rate significantly reduced after FSP also with an addition of W particles. A negligible reduction (1.83% IACS) in electrical conductivity was noticed for both Cu and Cu-W after FSP. This study demonstrates that the FSP is an effective approach to improve the surface mechanical properties of Cu without much impairing the electrical conductivity.

Kumar H., Prasad R., Kumar P., Hailu S.A.

The present work aims to develop Cu/ZrO2 surface composite by friction stir processing and analyse the effect of zirconia incorporation on microstructure, mechanical, and tribological behaviour of developed copper matrix composite. Microstructural observations indicated that grains were equiaxed and fine in the stir zone of the composite and zirconia particles were uniformly dispersed in the copper matrix with excellent bonding. The test results for mechanical and wear behaviour showed increment in hardness and wear resistance as compared to copper which may be because of the effect of zirconia presence and grain refinement. The fabricated composite displayed higher value of average friction coefficient in comparison to as received copper. The worn surface observed by SEM revealed the predominance of adhesion and delamination wear mechanism in base copper.

Sudhagar S., Gopal P.M.

Copper surface composite are gaining attention in recent years because of its tailor made properties. The current work emphasized on characterization of copper surface composite manufactured through solid state processing technique friction stir processing. The pure copper is used as matrix material and reinforced with Si3N4 particles at various volume percentages of 5, 10 and 15. The fabricated composites were tested to assess various properties such as microstructure, tensile, hardness and wear. The microstructure revealed that dynamic recrystallization is occurred during FSP under the action of rotating tool. Hardness and wear resistance of the composites were improved upon the addition of reinforcement particles. Addition of reinforcement reduces the tensile strength compared to unprocessed copper however strength increases with increase in volume percentage of Si3N4. Surface composite with 15 % Si3N4 shows higher hardness and wear resistance than other composites and pure copper.

Dadkhah M., Mosallanejad M.H., Iuliano L., Saboori A.

Nowadays, as an emerging technology, additive manufacturing (AM) has received numerous attentions from researchers around the world. The method comprises layer-by-layer manufacturing of products according to the 3D CAD models of the objects. Among other things, AM is capable of producing metal matrix composites (MMCs). Hence, plenty of works in the literature are dedicated to developing different types of MMCs through AM processes. Hence, this paper provides a comprehensive overview on the latest research that has been carried out on the development of the powder-based AM manufactured MMCs from a scientific and technological viewpoint, aimed at highlighting the opportunities and challenges of this innovative manufacturing process. For instance, it is documented that AM is not only able to resolve the reinforcement/matrix bonding issues usually faced with during conventional manufacturing of MMCs, but also it is capable of producing functionally graded composites and geometrically complex objects. Furthermore, it provides the opportunity for a uniform distribution of the reinforcing phase in the metallic matrix and is able to produce composites using refractory metals thanks to the local heat source employed in the method. Despite the aforementioned advantages, there are still some challenges needing more attention from the researchers. Rapid cooling nature of the process, significantly different coefficient of expansion of the matrix and reinforcement, processability, and the lack of suitable parameters and standards for the production of defect-free AM MMCs seem to be among the most important issues to deal with in future works.

Heidarpour A., Mazaheri Y., Roknian M., Ghasemi S.

In the search of enhancing the surface properties of metals, application of the friction stir processing (FSP) method could be a good choice. In this study, copper-TiO2 surface nanocomposite was successfully developed through FSP and the effects of pass number on its microstructure, mechanical properties, tribological and corrosion behavior were explored. To characterize the microstructure of the composites, optical microscopy (OM), and field emission scanning electron microscopy (FESEM) were utilized. Mechanical properties in the terms of microhardness and tensile test were investigated. Results showed that by increasing the pass number of FSP, a significant enhancement in mechanical properties of the samples has occurred. In comparison to the pure copper, the microhardness, yield and tensile strength values using 4-pass FSP were found to improve 77%, 33%, and 186%, respectively. In addition, increasing the FSP pass number led to the reduction of the sample's elongation. The wear properties of the surface composites were found to the great enhancement by increasing the pass number. In addition, the corrosion results showed that the surface nanocomposite after 4 passes FSP had much high corrosion resistance.

Shahedi B., Damircheli M., Shirazi A.

Mirjavadi S.S., Alipour M., Emamian S., Kord S., Hamouda A.M., Koppad P.G., Keshavamurthy R.

The aim of the current study is to investigate the effect of addition of TiO 2 nanoparticles and friction stir welding (FSW) parameter such as number of passes on microstructure, mechanical and tribological properties of friction stir butt-welded joints of AA5083 alloy plates. The experiments were performed on AA5083 alloy based composite plates at different rotational and forward speed in the range of 300–710 rpm and 14–28 mm/min respectively. The optimized high strength value based AA5083/TiO 2 composite plates were then subjected to different number of passes ranging from 1 to 4. These butt-welded regions of TiO 2 reinforced and unreinforced AA5083 alloy plates were characterized using optical and scanning electron microscope (SEM) to study the microstructure, dispersion of TiO 2 and grain size. The hardness and ultimate tensile strength of AA5083 composite after four passes with rotational speed of 710 rpm and forward speed of 14 mm/min was increased by 40% and 25% when compared to that of unreinforced AA5083 alloy. The wear characteristics of all butt-welded samples evaluated using pin on disc tribometer revealed better wear resistance and low friction coefficient for samples processed using four numbers of passes. The fractured tensile samples and worn out surfaces after wear testing were analyzed through SEM. The improvement in mechanical and wear properties are mainly attributed to reduced grain size, uniform dispersion of TiO 2 nanoparticles and dislocation strengthening.

Wąsik M., Karwan-Baczewska J.

Copper based Metal Matrix Composites are promising materials for electrical and electrotechnical applications such as electronic packaging and contacts, resistance welding electrodes, heat exchangers etc. Introducing the ceramics particles into the copper matrix allows to achieve a higher mechanical properties comparing to pure copper. The literature shows the variety of reinforcement materials are used. The most commonly strengthening phase include: oxides Al2O3,Y2O3, SiO2, carbides SiC, WC, TiC, ZrC, borides TiB2, ZrB2 and others such us volcanic tuff, carbon or intermetalic phases Al-Fe. [1-7]. It is obvious that reinforcement material without TiN leads to decrease the electrical conductivity of copper. Preliminary investigations concerning nanoscale Cu-based composites with TiN particles were presented in papers [10, 11]. Powder metallurgy (PM) process leads to obtain uniform distribution of strengthening phase in matrix. In order to achieve uniform distribution the process parameters such as mixing and selection the sizes of particles must be appropriate selected. The another factor of decreasing the mechanical and electrical properties by using PM route is porosity. Conventional PM process includes pressing and sintering does not always allow to achieve the high density what is one of the main criterion for high electrical conductivity material. The hard ceramic particles in metal matrix which are not deformable make difficult the densification process. In some cases the use of more advanced methods of production is desirable. The use of titanium nitride particles is justified by their high electrical conductivity in compare to the other reinforcement materials.

Purcek G., Yanar H., Demirtas M., Alemdag Y., Shangina D.V., Dobatkin S.V.

Properties of Cu–Cr–Zr alloy with ultrafine-grained (UFG) structure produced by equal-channel angular pressing (ECAP) via different routes have been investigated. Special attention was paid to the optimization of multi-functional structural, thermal, electrical and mechanical properties of the alloy by aging of UFG one. Multi-pass ECAP via different routes gives rise to the formation of a deformation-induced submicrocrystalline structure with the grain (subgrain) sizes in the range of 200–300 nm depending on applied routes which leads to high hardness and strength in the Cu–Cr–Zr alloy with reduced ductility. Amongst the applied routes, route-Bc was found to be the best processing path for achieving the lowest grain size, the highest hardness and strength. Aging of 8Bc-processed UFG samples increases the hardness and strength of Cu–Cr–Zr alloy while retaining an electrical conductivity comparable to that of aged coarse-grained (CG) one. A satisfactory electrical conductivity of 71%IACS without considerable loss of peak hardness was achieved after aging of 8Bc-processed UFG alloy at 425 °C for 240 min. The precipitation strengthened UFG alloy remains its stable behavior at elevated temperatures up to 450 °C.

Hernández-Pérez A., Eddahbi M., Monge M.A., Muñoz A., Savoini B.

An ITER-grade Cu–Cr–Zr alloy was subjected to equal channel angular pressing (ECAP) at 400 °C via routes BC and C, i.e. rotated 90° or 180° around the extrusion axis before subsequent passes. The microstructure of ECAP deformed samples showed shear bands confining small recrystallized grains of about ∼0.2–1 μm in size. The best mechanical properties were observed for sample ECAP processed via route BC for which the density of shear bands is high and the interaction among them is notable.

Li J., Wongsa-Ngam J., Xu J., Shan D., Guo B., Langdon T.G.

A Cu-0.1 wt.% Zr alloy was processed by equal-channel angular pressing (ECAP) through 8 passes at room temperature to produce an ultrafine grain size of ~350 nm with an average Vickers microindentation hardness (200 gf) of ~140. Ball-on-disc dry sliding tests were conducted on an annealed material and on the ECAP-processed alloy using applied normal loads from 1 to 15 N. The coefficient of friction (COF), surface topography and wear volume loss were examined to evaluate the micro-wear resistance. The results show that samples processed by ECAP have lower average values for the COF than the unprocessed alloy and there is also a decrease in the wear depth and wear volume loss with increasing numbers of ECAP passes. The ultrafine-grained alloy processed by ECAP has a higher wear resistance than the annealed and unprocessed material due to the significant grain refinement and improved mechanical properties.

SATHISKUMAR R., DINAHARAN I., MURUGAN N., VIJAY S.J.

An attempt was made to synthesize Cu/B4C surface composite using friction stir processing (FSP) and to analyze the influence of tool rotational speed on microstructure and sliding wear behavior of the composite. The tool rotational speed was varied from 800 to 1200 r/min in step of 200 r/min. The traverse speed, axial force, groove width and tool pin profile were kept constant. Optical microscopy and scanning electron microscopy were used to study the microstructure of the fabricated surface composites. The sliding wear behavior was evaluated using a pin-on-disc apparatus. The results indicate that the tool rotational speed significantly influences the area of the surface composite and the distribution of B4C particles. Higher rotational speed exhibits homogenous distribution of B4C particles, while lower rotational speed causes poor distribution of B4C particles in the surface composite. The effects of tool rotational speed on the grain size, microhardness, wear rate, worn surface and wear debris were reported.

Liu F., Tong B., Zhu R., Wei G., Dong K.