No abstract

Thermo-chemical technique was used to synthesize Cu-Al 2 O 3 nanocomposite powders. The process was carried out by addition of Cu powder to aqueous solution of aluminum nitrate. Afterwards, a thermal treatment at 850˚C for 1 hr was conducted to get insitu powders of CuO and stable alumina (Al 2 O 3 ). The CuO was reduced in hydrogen atmosphere into copper powder. The nanocomposite powders of both copper and alumina were thoroughly mixed, cold pressed into briquettes and sintered at 850˚C in hydrogen atmosphere. The x-ray diffraction and scanning electron microscope (SEM) with energy dispersive spectrometer (EDS) were used to characterize the structure of the obtained powders. The results showed that alumina nanoparticles (20 nm) and ultra fine copper crystallite (200 nm) were obtained. SEM and EDS showed that the alumina particles were uniformly dispersed within the copper crystallite matrix. The structure also revealed formation of a third phase (CuAlO 2 ) at copper-alumina interface. The hardness and density results showed that the gain in hardness was found to be dependent on the alumina contents rather than on the relative densities. The alumina content up to 12.5% resulted in an increase of 47.9% in hardness and slight decrease (7.6%) in relative densities. The results of compression tests showed considerable increase in compression strength (67%) as alumina content increased up to 12.5%. The compression strength showed further increase in compression strength (24%) as strain rates were increased from 10 -4 s -1 to 10 -2 s -1 . Strain hardening and strain rate parameters "n" and "m" have shown positive values that improved the total strain and they can be used to predict formability of the nanocomposite.

In situ chemical reaction method was used to synthesize Cu-ZrO 2 nanocomposite powders. The process was carried out by addition of NH 4 (OH) to certain amount of dispersed Cu(NO 3 ) 2 ·3H 2 O and ZrOCl 2 ·8H 2 O solution. Afterwards, a thermal treatment at 650 °C for 1 h was conducted to get the powders of CuO and ZrO 2 and remove the remaining liquid. The CuO was then reduced in preferential hydrogen atmosphere into copper. The powders were cold pressed at a pressure of 600 MPa and sintered in a hydrogen atmosphere at 950 °C for 2 h. The structure and characteristics were examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The results showed that the nanosized ZrO 2 particles (with a diameter of about 30-50 nm) was successfully formed and dispersed within the copper matrix. The density, electrical conductivity, mechanical strength measurements (compression strength and Vickers microhardness) and wear properties of Cu-ZrO 2 nanocomposite were investigated. Increment in the weight % of ZrO 2 nano-particles up to 10 wt.% in the samples, caused the reduction in the densification (7.2%) and electrical conductivity (53.8%) of the nanocomposites. The highest microhardness (146.5 HV) and compressive strength (474.5 MPa) of the nanocomposites is related to the Cu-10 wt.% ZrO 2 . Owing to the good interfacial bonding between uniformly dispersed ZrO 2 nanoparticles and the copper matrix. The abrasive wear rate of the Cu-ZrO 2 nanocomposite increased with the increasing load or sliding velocity and is always lower than that of copper at any load or any velocity.

In this paper, we present a newly modified machine learning model that employs a long short-term memory (LSTM) neural network model with the golden jackal optimization (GJO) algorithm to predict the tribological performance of Cu–Al2O3 nanocomposites. The modified model was applied to predict the wear rates and coefficient of friction of Cu–Al2O3 nanocomposites that were developed in this study. Electroless coating of Al2O3 nanoparticles with Ag was performed to improve the wettability followed by ball milling and compaction to consolidate the composites. The microstructural, mechanical, and wear properties of the produced composites with different Al2O3 content were characterized. The wear rates and coefficient of friction were evaluated using sliding wear tests at different loads and speeds. From a materials point of view, the manufactured composites with 10% Al2O3 content showed huge enhancement in hardness and wear rates compared to pure copper, reaching 170% and 65%, respectively. The improvement of the properties was due to the excellent mechanical properties of Al2O3, grain refinement, and dislocation movement impedance. The developed model using the LSTM-GJO algorithm showed excellent predictability of the wear rate and coefficient of friction for all the considered composites.

No abstract