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Abstract
Powder metallurgy (PM) has become a highly growing technology in the industrial world in the last two decades. This is ascribed to the fact that PM leads to an increase in productivity along with product efficiency and quality. Eventually, mixed powder sintering has many practical uses in automobiles, machinery, household, locking devices, fittings, and office appliances. It is a cost-effective route to composites and different grades of carbon and alloy steel with different compositions, each for specific application. Sintered steels based on Fe-Ni-C, Fe-Cu-C, and related chemistries are used in large quantities in the automotive industry where the inherent low cost is important
One of the major problems in automotive applications is the accelerating wear rate in friction components, such as gears, cams, and sprockets which results in short life of the equipment of concern. So, it has been necessary to give a solution to such a problem disturbing large category of manufacturers. Major solution introduced in this research is to increase the hardness of the metal of concern via addition of alumina powder, which has a high level of hardness and stability under sintering, to the Nickel PM Steel used extensively in such applications. The selection of such steel is based on the fact that it has the maximum toughness and ductility which are indispensable in this concern. Special care of preserving maximum density level and minimum dimensional change is not neglected.
A special die set to perform compaction of metal powder mixes has been designed and checked according to the specifications of material, shape and dimensions. Design check has been performed using finite element analysis (FEA) to predict stress, strain values under load of compaction and guarantee not to have buckling in the long free length members. Each die set component is assured to function properly during both compaction and ejection cycles.
Many experiments were carried out to study the effect of compaction pressure, sintering temperature and time. Different combinations of alloying additions were established. Carbon, copper, nickel, and alumina powders were added within the ranges accepted practically and approved by the literature. The experiments were performed on 55 work samples. Compaction process has been performed on the hydraulic press OMCN ART.164. Sintering process has been performed in the furnace SHUTTLE KILN K1354. A Central Composite Design of experiments was developed to organize the experiments and to investigate the effect of PM process conditions such as; percentage of each additive and compaction pressure on the product quality characteristics such as; hardness, density, and dimensional change from die size during compaction and sintering processes.
It has been concluded that the additions of alumina powder on nickel PM steels up to 1.0 wt. % show great improvement in hardness values reaching 37 % at 0.5 wt. % of alumina added to nickel PM steel matrix of the composition 2.3 wt. % nickel, 1.8 wt. % copper, and 0.7 wt. % carbon using 700 MPa compaction pressure and sintering temperature of 1200 °C for 30 minutes. Maximum possible density with minimum dimensional change was maintained. On the other hand, percentages> 1.0 wt. % alumina have a negative effect not only on hardness level but also the microstructure, density, and dimensional accuracy.