Dmitri Goljandin

High-temperature erosion of Fe-based coatings reinforced with cermet particles

High-velocity oxy-fuel sprayed, iron alloy-based powder coatings, reinforced with tungsten carbide–cobalt (WC–Co) and titanium carbide–nickel molybdenum (TiC–NiMo) cermet particles, are compared under high-temperature abrasive–erosive wear conditions. Both WC–Co and TiC–NiMo particles underwent fracture, as well as dissolution, during the spraying process, but in the case of WC–Co particles this process was remarkably less intensive. Under the low impact angle conditions, the WC–Co particle-reinforced coating exhibited 1.1 times lower wear than the TiC–NiMo particle-reinforced coating because of the larger amount of the reinforcement remaining. Under the normal impact angle conditions, the WC–Co particle-reinforced coating showed 1.2 times lower wear than the TiC–NiMo particle-reinforced coating because of the resulting larger size of the WC–Co reinforcement and a more ductile matrix.

Wear Behaviour of Recycled Hard Particle Reinforced NiCrBSi Hardfacings Deposited by Plasma Transferred Arc (PTA) Process

The main goal of present work was to study room temperature wear behaviour of advanced cermet particle reinforced hardfacings. For this purpose three different recycled powders: WC-Co, TiC-NiMo and Cr3C2-Ni were used as reinforcements for the commercially used NiCrBSi matrix alloy. Plasma transferred arc hardfacing process was used for deposition of the hardfacings. Manufactured hardfacings show only average wear resistance compared to WC/W2C reinforced NiCrBSi hardfacing with two times higher wear values. However, in combined impact/abrasive and erosive contacts, manufactured hard particle reinforced hardfacings have shown very promising results with high wear resistance. It was shown, that double structuring along with right material constituent and coating procedure selection may provide high wear resistance.

Recycled hardmetal-based powder composite coatings: optimisation of composition, structure and properties

Hardfacing is among the most economical methods for surface treatment and service life and efficiency improvement of metal parts subjective to wear. At the same time use of low-cost recycling technologies in the production of powders is of current interest. Focus in this paper is on: a) the production of hardmetal/cermet powders as reinforcements for composite coatings; b) deposition technologies and optimisation of coating structure; c) the wear resistance of coatings at different abrasive wear conditions. The article describes the production and grindability of hardmetal (WC-Co) and cermet (Cr3C2-Ni, TiC-NiMo) powders and their size and shape. Results address the optimisation of the composition and structure of HVOF-sprayed and PTA-welded composite powder coatings based on the commercial spray powders and produced hardmetal/cermet powders. The abrasive wear resistance of coatings at different wear conditions (rubber wheel, erosion and impact wear tests) is analysed.

Metallic powders produced by the disintegrator technology

The paper deals with the peculiarities of disintegrator milling, the development of disintegrator milling systems and the grindability of different metallic materials. In the first part of the paper the size reduction by collision is under consideration. A theoretical model for the size reduction of ductile materials by collision is proposed. The second part of the paper is focused on the development of disintegrators for processing of materials, which differs significantly from the other grinding equipment. The third part of the paper is focused on the disintegrator milling technology used for mechanical treatment of different metallic materials.

Optimization of Structure of Hardmetal Reinforced Iron-Based PM Hardfacings for Abrasive Wear Conditions

This paper focuses on the influence of hardmetal reinforcement amount, shape and size on the abrasive wear resistance of composite iron self-fluxing alloy (FeCrSiB) based hardfacings produced by the powder metallurgy (PM) technology. First, the size of the reinforcement (1 – 2.5 mm) was fixed, but its shape (angular or spherical) and amount (0 – 50 vol%) were varied. Then the reinforcement shape (angular) and amount (50 vol%) were kept constant, while its size (0.16 – 0.315 mm fine reinforcement and 1 – 2.5 mm coarse reinforcement) and proportion of fine and coarse reinforcement (all fine, all coarse, half fine-half coarse) were varied. ASTM G65 abrasive rubber wheel wear test was applied to find out the wear resistance of the hardfacings; an unreinforced self-luxing alloy (FeCrSiB) hardfacing was the reference material. Volumetric wear rate was calculated according to the weight loss. Worn surfaces were studied under scanning electron microscope. As a result, an optimal composition of the hardmetal containing Fe-based hardfacings based on the reinforcement amount (vol%), shape (irregular or spherical) and size (fine or coarse) is given.

The Properties of Mineral Additives Obtained by Collision Milling in Disintegrator

Mineral additives are materials which are used in wide range of industries including construction, cosmetics, agricultural and biotechnology. Such materials as plasters, paints, abrasives etc. are produced using mineral powders. Main qualities of mineral additives are purity of chemical composition, grading properties and shape factor. To obtain powder like material most common method is milling. One of most effective milling method for refining of brittle material is grinding by collision in disintegrator. One of advantage of this method is that high milling energy is transferred to the milling material in short period of time. In present research three types of mineral materials were treated in disintegrator with specific energy Es applied 8.4 and 25.2 kWh/t: natural quartz sand 0.3/1mm, quartz-limestone 0.3/2.5mm sand and dolomite screenings 0/4mm. Results indicate that powder like material with d90 form 66 to 141 µm could be obtained at Es 8.4 kWh/t while increase of Es reduces d90 value to 48 to 72 µm and the milling efficiency was effected by the sand type.

Characterization of Mechanical Milling Cermet Powders Produced by Disintegrator Technology

The current paper deals with characterization of TiC−NiMo cermet powders produced by mechanical milling technology. TiC-based cermets scrap was processed by semi-industrial and laboratory disintegrator milling system. Chemical composition, shape and size of produced powders were analyzed. To estimate the properties of recycled cermet powders the sieving analysis, and angularity studies were conducted. The grindability was estimated using specific energy parameter (Es). Considering that viewpoint, the study is focused on angularity studies as the shape of spray powder has considerable influence on spraying efficiency, the quality and reliability of the coating. To describe the angularity of milled powders, spike parameter – quadratic fit (SPQ) was used and experiments for determination of SPQ sensitivity and precision to characterize particles angularity were performed. Uncertainty of measurements demonstrated trustworthiness of results. The standard deviation of SPQ regardless of milling cycles is the same. For use of produced powders as reinforcements in sprayed coatings the technological parameters of powders were studied. Perspective future use of powders as reinforcements in composite coatings as well as abrasives in tooling were demonstrated.