The Properties Of Flame-sprayed Nylon1010 And Its Composite Coatings

Flame spraying is a process in which a metallic or non-metallic material is heated and then propelled onto a substrate to produce overlay coatings for protection or performance enhancement purposes. The simplicity of the process allows the coating can be applied in the field, which is very cost effective. In addition, there is no limitation on shelf or pot life.Polyamide (PA) is a kind of high performance thermoplastic material. It becomes of great interest to applications as bearing and slider materials. PAIOIO is one of the long carbon chain polyamides with excellent properties like wear-resistance and corrosion-resistance etc. On the other hand, nanometer-sized particles have superior properties compared to conventional materials. However, little research on the flame-sprayed PAIOIO and its composite coatings. In this thesis, we report our investigations on the properties of flame-sprayed PAIOIO coatings with and without the incorporation of nanometer-sized particles such as silica (n-SiO2), titanium oxide (n-TiO2), zinc oxide (n-ZnO) and graphite (n-G).In the first part of the thesis, we have established a method for the first time for measuring the adhesive strength and cohesive strength about flame sprayed polymer coatings. We have designed two suites of moulds, one is for measuring the adhesive strength between the coatings and the metal substrates and the other is for measuring the cohesive strength of coatings. Results showed that the moulds are suitable to measure the strength of coatings. Both the adhesive and cohesive strengths of PAIOIO composite coatings with n-TiO2, n-ZnO, n-SiO2 and n-G was improved due to the incorporation of nanometer-sized materials.Using a uniform experimental design method, the dry friction and wear behaviors of PAIOIO and its composite coatings with graphite (G) and n-SiO2 were systematically investigated under dry sliding conditions against TMK rings by a ring-cube wear-test machine of MRH-3. The tests were performed at room temperature under air environment. The applied load (P) and sliding velocity (V)were selected according to the uniform design. Each test lasted for 20min and the weight loss was measured using an electronic scale. And the statistics of regression analysis of the experimental results was performed using software of SPSS 11.0 for Windows. The dry friction coefficient between the coating and steel increased while increasing the PV volume in some extent; when the PV volume increased beyond some value, the dry friction coefficient became decreased. The wear mass loss change with the PV volume was in the similar trends with that of dry friction coefficient. The wear mechanism of the coating was explained in terms of plastic deformation, fatigue tearing and adhesive abrasion.Due to the excellent thermal conductivity and lubricity of graphite, the friction surface temperature might be decreased and friction stress be diffused. Therefore, the incorporation of graphite improves the friction resistance of PA1010 coating greatly. SEM observations revealed that n-SiO2 can diffuse the friction stress and check the occurring of friction cracks, the worn surfaces of composite coatings with n-SiO2 were much smoother than that of pure PA1010 coating, the friction and wear resistance of PA1010 coating was improved obviously by the incorporation of n-SiO2. Ageing tests showed that the composite coatings with n-SiO2, n-TiO2 and n-ZnO have better age resistance than pure PAIOIO coating, and the composite coating with n-TiO2 has the best ageing property.