Processing and Characterization of Extremely Hard and Strong Cu-(0-15 wt pct)Al Alloys MAHAMMAD ALI SHAIK, BRAHMA RAJU GOLLA, and SURESH BABU PITCHUKA The present work investigates the microstructure development and mechanical properties of mechanically alloyed and hot-pressed copper (Cu)-X wt pct aluminum (Al) (X = 0, 3, 5, 10, 15) alloys. The morphology of the ball-milled Cu-Al powders changed from coarse flaky structure to small hard agglomerates with the addition of Al. It was observed that the density of Cu-Al samples varied between ~ 95 and 98 pct of theoretical density (q th ) after hot pressing (Temperature: 500 °C, Pressure: 500 MPa, Time: 30 min). The crystallite size of Cu-Al samples decreased for both the milled powders and hot-pressed samples. The XRD and SEM-EDS analyses of the hot-pressed samples confirmed the presence of a-Cu solid solution phases for the Cu alloyed with Al up to 5 wt pct. On the other hand, further addition of Al to Cu leads to the formation of both intermetallic compound (Cu 9 Al 4 ) and solid solution phase. The nano-in- dentation tests indicated a significant increase in hardness (2.4 to 7.9 GPa) and elastic modulus (121.1 to 177.4 GPa) of Cu-Al alloys. The Cu-Al alloys were measured with very high compressive strength (813.8 to 1120.2 MPa) and the compressive strain varied in the range of 29.81 to 5.81 pct. https://doi.org/10.1007/s11661-019-05545-x Ó The Minerals, Metals & Materials Society and ASM International 2019 I. INTRODUCTION COPPER (Cu) alloys have been extensively used for various engineering applications such as naval, rail, aerospace, and automobile industries. In particular, braking and electro-discharge machining (EDM) elec- trode applications require the development of Cu alloys with high strength, good conductivity and workability, structural stability at high temperatures (~ 200 °C to 450 °C), good wear, oxidation, and corrosion resis- tance. [1,2] In fact, Cu has been alloyed with alloying elements such as Zn, Sn, Al, W, Fe, Cr, and Zr and these alloys were mainly strengthened by solid solution strengthening or precipitation hardening mecha- nisms. [3–8] Traditionally, these Cu alloys were processed by casting route. [9] One of the major disadvantages of traditional Cu alloys processed by casting route was the coarse grain structure that will lead to poor mechanical properties. Hence, it is required to use alternative processing techniques in order to control the grain size and improve the mechanical properties of Cu alloys. Severe plastic deformation (SPD) techniques such as high-pressure torsion (HPT), [8–10] equal channel angular pressing (ECAP), [11] twist extrusion, [12] accumulated roll bond- ing, [13] repetitive corrugation and straightening, [14] cryo-rolling, [15] and friction stir processing (FSP) [16] were extensively reported for Cu and its alloys. Powder metallurgy (PM) processes [including Mechanical alloy- ing (MA), spark plasma sintering (SPS)] and additive manufacturing methods [such as selective laser sintering (SLS) and selective laser melting (SLM)] have also been attempted to produce Cu alloys with fine structure. [4,6,17–20] In particular, in view of its nonsparking characteris- tics, good wear and corrosion resistance, the Cu-Al alloys have potentiality for a range of applications such as welding electrodes, tool material for sheet forming, bearings, rocket nozzle, heat sink, automobile, mining, and naval engineering applications. However, in the literature, studies on Cu-Al alloys have been consider- ably low and, in particular, systematic investigation of Al effect on the microstructure and mechanical proper- ties of Cu processed via PM route. Calvo et al. [21] studied the effect of pressure and temperature on bonding between Cu and Al. Their work revealed that the bonding between Cu and Al was mainly dominated by diffusion mechanism (between 400 °C and 520 °C and up to 289 hours). The diffusion bonding between MAHAMMAD ALI SHAIK and BRAHMA RAJU GOLLA are with the Metallurgical and Materials Engineering Department, National Institute of Technology, Warangal, 506 004, India. Contact e-mails: gbraju121@gmail.com; gbraju@nitw.ac.in SURESH BABU PITCHUKA is with the International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI) Hyderabad 500005, India. Manuscript submitted April 24, 2019. METALLURGICAL AND MATERIALS TRANSACTIONS A