Corrosion Resistance of Nickel-Based Composite Coatings Reinforced by Spherical Tungsten Carbide

Nickel-based composite coatings reinforced by spherical tungsten carbide were deposited on 42CrMo alloy steel using plasma transfer arc welding (PTAW) process. Their electrochemical corrosion properties in NaCl solution under atmospheric and high pressure were studied by polarization curve, electrochemical impedance spectroscopy. The corrosion and erosion resistance of the coatings were also investigated by salt spray corrosion and erosion corrosion tests. The results show that the self-corrosion potential of the composite coatings increased with the increase of tungsten carbide content, and the Cr element in Ni60 sample formed a stable and compact passivation film. Compared with corrosion at atmospheric pressure, the adsorption and penetration of Cl- on the coating surface enhanced due to the increase of Cl- activity under pressure, thereby to weaken the corrosion resistance. The Samples that passivated in salt spray environment, cannot completely hinder the corrosion of the coating, just only to slow down the corrosion. This study can provide theoretical basis for deep-sea oil drilling and production engineering equipment.

Original Experimental Campaign of Indentation Instrumented on Aggregates of Non-Hazardous Waste Incineration Bottom Ash to Study the Heterogeneity of their Rigidity

An extensive experimental work of instrumented indentation on isolated particles of Non-Hazardous Waste Incineration bottom ash (NHWI) is presented in this paper. The aggregates studied come from the Garenne quarries at Vignoc (Brittany, France). Two spherical tungsten carbide indenters of respective 0.5 and 140 mm radius “R” were used for test series “A” and “B”. The particles studied have diameters ranging between 20 and 25 mm. With a 0.5 mm radius indenter, average reduced elastic moduli ranging from 15 to 68 GPa were found. An average reduced elastic modulus of 15 GPa was found with the 140 mm radius indenter. The experiments made it possible to highlight the particular heterogeneity that characterizes the rigidity of the types of aggregates studied.

New Equipment for Production of Super Hard Spherical Tungsten Carbide and other High-Melting Compounds Using the Method of Plasma Atomization of Rotating Billet

In order to ensure high wear resistance of parts and tools, operating at significant dynamic loads in the extreme conditions, the layers different in their function purpose obtained using surfacing methods are widely used. In such surfacing compositions, the powders of high-melting compounds characterized by high hardness and strength, are used as a wear resistant component, for example, alloys of tungsten carbide WC + W2C (cast tungsten carbide), and as binder matrix the plastic and metal alloys are used.The great interest is the development of methods allowing producing powders of cast tungsten carbide and other high-melting-point materials of uniform composition, characterized by a high sphericity of the particles and having higher physical-mechanical properties. The spherical tungsten carbide was produced by plasma atomization of rotating billet. The universal installation for production of super-hard spherical tungsten carbide and other high-melting-point compounds by plasma atomization of rotating billets was designed for industrial application. The results showed that the application of the technology of plasma rotary atomization of rotation billet to obtain granules of powders of high-melting-point materials was promising, in particular tungsten carbide with sphericity over 90%, microhardness HV0.1 more than 3000 kg / mm2 characterized by high flow ability more than 7.5 s/ 50 g. Due to the use of new materials and innovative design and technological solutions the high reliability, maximum interval of technical service, high resource of operating units and executing mechanism of the equipment were ensured. Due to the use of new high-power plasma system with power supply source with high efficiency coefficient and improved dynamic characteristics, the system of preliminary heating of billets, innovative gas systems, high performance vacuum system, the developed universal system for the production of granules of powders of high-melting-point material were also applicable for the manufacture of spherical powders of metals and alloys, including highly active, and provided lower costs of products (powder) with an increased productivity, economic efficiency of the atomization process and reduced the impact of atomization process on the environment.

Fracture modes in curved brittle layers subject to concentrated cyclic loading in liquid environments

Damage response of brittle curved structures subject to cyclic Hertzian indentation was investigated. Specimens were fabricated by bisecting cylindrical quartz glass hollow tubes. The resulting hemicylindrical glass shells were bonded internally and at the edges to polymeric supporting structures and loaded axially in water on the outer circumference with a spherical tungsten carbide indenter. Critical loads and number of cycles to initiate and propagate near-contact cone cracks and far-field flexure radial cracks to failure were recorded. Flat quartz glass plates on polymer substrates were tested as a control group. Our findings showed that cone cracks form at lower loads, and can propagate through the quartz layer to the quartz/polymer interface at lower number of cycles, in the curved specimens relative to their flat counterparts. Flexural radial cracks require a higher load to initiate in the curved specimens relative to flat structures. These radial cracks can propagate rapidly to the margins, the flat edges of the bisecting plane, under cyclic loading at relatively low loads, owing to mechanical fatigue and a greater spatial range of tensile stresses in curved structures.