Surface melting and alloying of commercial complex aluminium bronze CA104 has been carried out using an electron beam. In addition, other aluminium bronzes - Ampco 18, Ampco 25, CMA1 and AB2 have also been surface melted. The structural changes have been studied using optical microscopy, scanning and transmission electron microscopy, energy dispersive X-ray analysis and X-ray diffraction analysis. The hardening response to the treatments and the hardening mechanisms have been investigated. Tempering of the surface melted CA104 has also been carried out systematically to investigate the responses of the structure and hardness to subsequent heat treatment. The wear behaviour of the materials has been studied in both dry and lubricated rolling-sliding contact against hardened En19 steel and under two-body abrasive conditions against silicon carbide grinding papers. The electrochemical corrosion properties in simulated cooling water and 3.5% NaCI solution have been studied using AC impedance and DC polarisation techniques. Experimental results show that the surface layers have been transformed to martensitea fter surfacem elting due to rapid solidification and fast subsequenct ooling. The martensite in the surface melted CA104 has a 3R structure with globular precipitates dispersed in it, which are based on (Ni, Fe)A1 with a B2 structure. On subsequent tempering treatment, these precipitates grow steadily with increasing temperature and time and the martensite gradually transforms to copper-based solid solution. The hardness has been increased by surface melting as a result of the martensitic transformation and precipitation hardening. During tempering, further precipitation hardening occurs and the hardness shows a peak plotted against temperature. Surface alloying with aluminium can increase the hardness beyond that achievable by surface melting. The tungsten carbide retained after surface alloying further strengthens the alloy. The wear rate and the friction coefficient in both the dry and lubricated rolling sliding wear have been reduced by surface melting. In the dry wear test, adhesive and delamination wear are the main wear mechanisms while it is abrasive wear that dominates the lubricated wear. The abrasion resistance against silicon carbide has been increased by both surface melting and alloying, with surface alloying much more effective. The best abrasionr esistanceis obtainedf rom the material alloyed with WC particles. The results also show that the electrochemical corrosion properties are improved by surfacem elting in both electrolytesu sed. The charget ransfer resistanceis increaseda nd the corrosion current is reduced. In the simulated cooling water, the corrosion of the materials during anodic polarisation follows three steps: the formation of cuprous oxide layer on the surface; the damage and destruction of the oxide layer; the pitting and the formation of the main corrosion product, CuCl.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:526761 |
| Date | January 1995 |
| Creators | Shi, Z. |
| Publisher | University of Birmingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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