Coatings which control adhesive strength in a metal-polymer system

Abstract

621.792In creating composite materials, glued joints, and also in preparing production equipment for casting and pressing polymers considerable attention should be devoted to choosing the composition of intermediate layers and coatings which control the adhesion reaction between metal and polymer.The adhesion reaction has been studied 1 for polymers with coatings of three types on carbon steel: carbide (based on chromium carbide alloyed with vanadium and boron), boride (based on iron boride), and nitride (based on titanium, vanadium, and chromium nitrides). Carbide and boride coatings were prepared by diffusion impregnation of specimens of steel U8 (0.8 % C) in powders and containers with a molten seal, and nitride coatings were prepared by the ion-plasma method (the CIB method, i.e., condensation of a coating from a plasma phase with ion bombardment). A study was made of the structure, chemical, and phase composition, and also the properties of coatings (microhardness, microbrittleness, adhesive reaction with the polymer). Metallographic analysis was performed in light (Neophot-21) and scanning electron (Cam Scan) microscopes with magnifications of ×400-8000. The chemical composition of coatings was determined in an Cam Scan electron-probe microanalyzer, and the phase composition was determined in a DRON-3 diffractometer in cobalt and copper Ks-radiation (Table l).The microbrittleness of coatings was evaluated by a procedure [1] which is based on measuring microhardness in a PMT-3 instrument: The relative number and nature of impressions with cracks of the total number was determined with an increase in load from 0.196 to 1.96 N (overall scale of brittleness Zp) and the rate of increase in brittle failure was calculated with an increase in load (aZ/0P)p.The material brittleness index (yp) reflecting the nature of brittle failure and the rate of its development with an increase in load considers [1] production of an overall scale of brittleness by the value of derivative with respect to load: yp = Zp(0Z/0P)p.Metallographic analysis showed that the thickness of diffusion coatings (15-65 ~m) was greater than for ion-plasma coatings (4.5-7.5 ~m). Carbide and nitride coatings have the lowest brittleness, and boride coatings have the greatest. At the same time the brittleness of the coatings studied did not exceed that of many metal phases [1].The adhesive strength of the 'metal (coating)-polymer' contact was determined by a procedure given in [2]. Adhesive reaction arises at the contact surface of a steel wire 0.5 mm in diameter with a layer of adhesive: polyethylene or epoxy compound I~DT (based on I~D-20). A coating is previously formed on the surface of the steel wire (steel U8) by diffusion (contact gas) and ion-plasma methods. The wire with a coating is held in the molten polyethylene at 200°C for 4 h or I~DT at 160°C for 6 h.With the failure of specimens the force (P) is measured required for pulling the wire out of the adhesive layer, i.e., the shear adhesive strength is determined: r = P/S, where S is coatin...