Abstract
Optimisation of thermal spraying, as for generic polymers, produces thermosets in the uncured condition with unsatisfactory engineering properties. The present paper develops a theoretical process modelfor thermoset reactive deposition, based on heat transfer mechanisms, which enables temperature profiles to be generated as a function of process variables. The model predicts that crosslinking can not take place in in flight precursor particles, isolated splats, or deposits without substrate preheating. It shows that the difficulty in achieving satisfactory properties is a result of the rapid heat flow to the substrate, which suppresses the crosslinking reaction. The model is applied to identify methods of enhancing the engineering properties of thermosets and indicates that substrate preheating, ceramic undercoats, and rapid curing agents can promote the curing reaction during thermal spraying. An experimental technique to evaluate the degree of crosslinking in the deposits from enthalpy determinations is developed. The experimental work, which consisted of differential scanning calorimetry and tribological measurements, is in agreement with the theoretical model and the predicted process route was successful in producing thermosets that were 85% cured in situ by reactive deposition.
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