Iron-based hardfacing alloys are widely used to counteract abrasive and impact wear of industrial components soil in, sand and mineral processing applications. These alloys show a high performance to cost ratio as well as a low environmental impact. The wear resistance of the components hardfaced with these alloys depends on achieved coating microstructure i.e. on the alloys chemical composition, the coating method and process parameters selected. The present work focuses on iron based hardfacing alloys with varying amount of chromium, vanadium, tungsten, molybdenum, boron and carbon deposited by plasma transferred arc (PTA) overlay welding. Weldability, hardness, abrasive and impact wear of the overlays are presented and interpreted through their microstructure. The performance of the iron based overlays is compared with that of nickel-based metal matrix composite coatings with tungsten carbide (MMC) commonly used for hardfacing of parts subjected to severe abrasive wear. The hardness of the iron based overlays investigated ranges between 60 and 65 HRC while abrasive wear is typically below 20 mm 3 (ASTM G65, procedure A). Microstructure consists of different primary precipitated carbides or borides, a martensitic matrix and eutectic structures.

Laser cladding technology is widely used in industry to precisely apply tailored surface coatings, as well as three-dimensional deposits for repair and additive layer-by-layer fabrication of metallic parts. However, the processing of larger components, like tools for oil and gas production, is economically challenging due to the conventionally low deposition rates. Consequently, industry is requesting more powerful technologies that maintain the quality advantages of the laser technology, but also make the process more productive and time effective. The modern highest power diode lasers offer practical solutions for applying of large-area laser cladding with significantly increased productivity. Using a fiber-coupled diode laser of 20 kW power and the accordingly developed laser cladding heads, real deposition rates of metal alloys, e.g. Inconel 625, could reach 14 kg/h. With the new-developed powder nozzles with rectangular profile of the powder jet allows at a laser power of 20 kW single tracks with 45 mm-width can be produced. Besides the laser source, the processing laser head is the key parameter for a high productivity and efficiency of the whole cladding procedure. The paper presents a new generation of high-performance laser cladding heads with integrated process sensors, which guarantee a stable long-time operation at highest power levels. The deposition rates achieved with this technology are equal or even exceed typical values of the common PTA technique. Current applications are large-area coatings on power plant components, hydraulic cylinders for off-shore equipment, and large metal forming tools for automotive bodies.

The powder of HSS (HSS23, AISI M3:2) was deposited by pulsed-PTA method on to low alloyed steel substrate. The influence of pulsation frequency was evaluated on the surface of deposits and on their cross sections by both light microscope and by Vickers hardness measurement apparatus and extreme properties mapping (XPS). Surfacing parameters at current frequency from 0 to 200Hz were tested during deposition of single weld bead. Dilution and heat affected zone were evaluated and compared for all tested parameters. The presence of retained austenite after deposition was determined by X-ray diffraction. The beads deposited with different frequencies differ in their shape, dilution degree, microhardness and penetration depth. It was found that the microhardness increases with current frequency.

Tungsten carbide in nickel based self-fluxing alloy overlays has been dominating hardfacing applications due to its excellent properties, namely extremely high wear resistance. Nevertheless, there are still applications and limits which tungsten carbide has not conquered. This study focuses on (TiW)C 1-x which was deposited with several matrix materials and tested in wear, corrosion and impact resistance and benchmarked against tungsten carbide. Results for several other carbides such as (NbW)C 1-x , (VW)C 1-x , NbC 1-x and TiC 1-x overlays deposited by plasma transferred arc (PTA) and laser cladding (LC) will be presented and discussed. As a result of deposition trials and overlay testing, it was found that better thermodynamic stability of alloyed carbides allows them to be used in an iron based matrix and/or a matrix with a high chromium content, in applications requiring improved corrosion and oxidation resistance, better impact resistance and lower weight.

Different types of tungsten carbide materials (fused tungsten carbide, nickel clad fused tungsten carbide, macrocrystalline WC and sintered and crushed WC/Co) are used for laser dispersing of construction steel surfaces. Surface roughness analyses and metallographic evaluation of cross sections concerning efficiency of carbide embedding as well as crack formation tendency are carried out. Generally, all types of tested carbides permit production of rough surfaces with metallurgical bonding to the metallic matrix, but only use of nickel clad fused tungsten carbide permits to prevent crack formation. The effectiveness of silicon and silicon carbide for production of durable rough surfaces on aluminium alloys is investigated. Both silicon and silicon carbide qualify for production of rough surfaces by laser dispersing. While silicon carbide particles show higher hardness, use of silicon does not include danger of embrittlement due to formation of aluminium carbide.