A common method to combat abrasive wear and prolong the life of a component is to hardface the exposed region by overlay welding. State of the art coatings for these applications consist of a nickel-based ductile matrix with hard tungsten carbide particles embedded in it. An alternative with low environmental impact in combination with high performance to cost ratio is to use iron-based alloys. Critical in affecting the abrasive and impact wear resistance of these alloys is the coating quality e.g. porosity, cracks, dilution from the substrate combined with chemistry, size and volume fraction of the hard phase particles formed during solidification. Selection of the process parameters is critical for producing sound clads with expected properties. This paper focuses on the properties of PTA welded and laser cladded M2, M4 and A11 high speed steel coatings. Clad quality, hardness, abrasive wear resistance and microstructure are presented and interpreted with support of thermodynamic simulations.

Highly wear resistant overlays for abrasive environments can be provided by welding technologies such as Plasma Transferred Arc Welding (PTAW) or Laser Cladding. Therefore, these overlays can contain higher amounts of hard particles with a desired homogeneous distribution through the weld overlay, all embedded in a metal matrix. Depending on the welding technology, the dissolution of the hard particles has to be considered as result of heat input and chemical reaction between hard particles and metal matrix while welding. Cast Tungsten Carbides (CTC) in self-fluxing Ni based alloys are widely used and accepted compositions and allow to target requirements such as hardness, impact toughness and/or corrosion resistance if required. This investigation compares CTC with Macroline Tungsten Carbide regarding abrasive wear resistance in Ni, Co and Fe based alloys applied by PTAW and Laser cladding and gives an outlook on potential new solutions for wear resistance in abrasive conditions. Beside the relative wear resistance, this investigation also focusses on the seam thickness as reaction zone between the carbide particles and the metal matrices. A first SEM and EDX analysis of a worn surface and precipitated phases provides an explanation regarding wear behavior in abrasive conditions.

This study ranks a number of common thermal surfacing materials for soil tillage applications based on the results of dry-sand rubber-wheel testing for abrasion resistance. Test specimens were prepared by plasma transferred arc (PTA) and powder welding deposition of a nickel-based self-fluxing matrix with and without tungsten carbide (WC) additions. For comparison, PTA coated M2 tool steel and quenched and tempered spring steels were also tested. PTA and PW deposition produced coatings with a similar level of abrasive wear resistance. Hardfacing with M2 and nickel-based 1560 deposited by PTA showed ~30% and ~15% wear respectively compared to the reference steels, while nickel-based grades with additions of 50% carbide showed only ~5% wear. Moreover, by increasing the amount of WC from 50 to 60 wt%, abrasive wear resistance was increased by 25%.

The specific advantages of TiC as a hard material are its low density, high hardness and the high alloyability of the hard phase - binder metal composite. Currently developed agglomerated and sintered core-rim structured TiC-based powders were intensively studied in the last few years for thermal spray coating solutions. In the work described in this paper two different powders with cubic (Ti,Mo)C and (Ti,Mo)(C,N) hard phases and Ni/Co binder, representing the first and second alloying step for the binary TiC-Ni/Co composite, were used together with mechanically mixed NiBSi powder to produce wear resistant coatings by plasma-transferred arc welding (PTA) and laser cladding. Basic process parameters, coating microstructures and properties are described. Coatings with fine grained hard particles were obtained by both processes, while the coating prepared from the nitrogen-containing powder by laser cladding shows a significant smaller hard particle grain size and increased hardness.

Plasma Transferred Arc (PTA) welded coatings are used to improve surface properties of mechanical parts. Advantages are the high reliability of the process and the low dilution of substrate and coating material. Processing of surfaces by PTA welding is restricted at the time to flat horizontal position. Furthermore industry is interested in the development of strategies for coating with PTA in constraint position as complex 3-D parts could be then easily processed as well. Under commercial aspects, the process design can be optimized in order to increase process efficiency and to reduce heat input during the welding process. Process optimization involves the determination of guidelines for PTA welding in constraint positions as well. Modelling the process gives an alternative to reduce the experimental effort to optimize the welding process. Results of simulation studies of the PTA welding process will be given in the present work. It will be shown, that coating conditions can be optimized by varying plasma gas flow, heat input and heat flow, process speed or powder injection with regard to welding in constraint positions. The defined controlling of the PTA welding allows to modify process management with less experimental effort and to develop coating strategies for processing in different positions. In experimental investigations the developed coating strategies will be confirmed by producing PTA coatings in constraint position as well as complex 3-D parts.

Plasma transferred arc welding (PTA) is used to produce coating for wear resistance application in earth moving equipment. The coating is designed to have balanced toughness and hardness, optimal microstructure to perform in the wear modes the components are subject to. 4~ 6 times improvement in wear life compared with hardened steel was achieved as demonstrated in dry sand/rubber wheel test and Caterpillar proprietary abrasion wear test

The exceptional properties of beryllium (Be) including low density and high elastic modulus, make it the material of choice in many defense and aerospace applications. However, health hazards associated with Be material handling limit the applications that are suited for its use. Innovative solutions that enable continued use of Be in critical applications while addressing worker health concerns are highly desirable. Plasma Transferred Arc solid freeform fabrication is being evaluated as a Be fabrication technique for civilian and military space based components. Initial experiments producing beryllium deposits are reported here. Deposit shape, microstructure and mechanical properties are reported.

The industrial set of PPAW-cladding has gained a higher importance in the last few years. The process is characterised by high quality layers of about 1-2 mm with a low dilution of about 5 % and without intermediate layers. The great amount of different alloys, which can be processed as powders, opens a wide range for industrial applications. Manually PTA-cladding can be performed in different working positions. Presently the full mechanised PTA-cladding process is carried out in horizontal position. Thus the components have to be moved relative to the plasma arc. In order to improve operating efficiency and flexibility when processing wear and corrosion resistant coatings it is necessary to enlarge the working area and to set strategies for cladding in constrain position. The effect of the gravitation force leads in this case to a very difficult governing of the pool, which flows downwards and affects the quality of the coating. Basic knowledge of the mechanised process depending on the cladding position, for example with industrial robots, is not available at the moment, even if this is necessary when cladding huge heavy components. The present work shows coating strategies as well as the influence of process parameters while cladding steel with corrosion and wear resistant powders in constrain position (bottom-up and top-down). Investigations with Ni- and Co-based alloys were examined and the suitability for constrain position was evaluated. Through an optimisation of the heat input it was possible to influence positively the melt flow and to carry out successfully coatings. Finally the transferability was successfully proven on a complex three dimensional component.

HVOF-, arc- and plasma sprayed coatings are widely used for wear protection. Today these type of layers are dominant if thin coatings from 50 up to 500 µm and low heat input into the work piece are required. The main disadvantage of thermally sprayed coatings is the adhesion to the substrate and the early failure when cyclic loaded. In both cases a metallurgical bonding to the substrate can improve the life cycle time. Plasma transferred arc (PTA) welded coatings show a metallurgical bonding to the substrate. The main disadvantages of this coating technology are the dilution of about 5%, the heat input into the substrate and that nowadays all welding positions seem to be impossible to carry out. In this paper the theoretical background for welding thin coatings (less than 500 µm) with a decreased dilution and in all welding positions is given and experimentally proved.

The unique wear protection properties of tungsten carbide metal matrix composite materials are resulting in their increasing use in the oilsand industry to combat severe low stress sliding abrasion and various types of slurry abrasion and erosion. Their successful application, mainly in bulk welding and spray coating forms, has extended component service lives, improved reliability and reduced maintenance costs. Increased use of tungsten carbide metal matrix composite hardfacing deposits in oil sands applications is the direct result of understanding carbide thermal degradation and the processes used to deposit these materials. Plasma transferred arc welding (PTAW) has proven to be an effective process for applying these materials. Current and future work on PTAW and other candidate processes to establish the optimum carbide hardfacing method will be reviewed.

The aim of this investigation is to increase the corrosion and wear resistance of magnesium (Mg) alloys. This paper explains how various coatings applied via plasma powder (PTA) and laser deposition welding processes affect the wear properties of two Mg alloys. It is shown that coating quality depends on the type of Mg used, the composition of the filler materials (matrix and carbides), and welding parameters. The best results for Mg alloys AM50 and AZ31 were obtained with a coating consisting of a composite matrix (AlSi 12 ) with boron carbide additions. Paper text in German.

This paper discusses some of the recent improvements in plasma powder surface build-up welding technology and provides examples of its use in different areas of industry. It describes the coating properties achievable with newly developed filler alloys and how they compare with conventional hardcoats. It also discusses the growing use of manual overlay PTA welding among small and midsize companies and the factors behind it. Paper text in German.

Extensive laboratory testing and field usage have shown that innovative surfacing techniques have produced cost effective maintenance systems and are providing long-term benefits. Self-fusing (sometimes known as self-fluxing) alloys containing tungsten carbide (WC), applied by PTAW, HVOF and SF (Spray Fusion) brazing processes are investigated. The process used and the effect of process parameters on the wear resistance of these coatings is evaluated. The test results show that the same self-fusing alloy applied by SF compared to PTAW have proven superior in severe erosive and abrasive applications. The case histories presented will cover a variety of applications including the use of HVOF versus hard chrome plating and the improvement in wear resistance of SF applied self-fused coatings versus PTAW. These comparisons are useful in providing new, higher performance solutions, in helping to overcome today's tougher surfacing and environmental requirements

Plasma transferred arc (PTA) is now currently used for reclamation of worn materials or to provide wear or corrosion resistant coatings welded to the base material. Instead of injecting the powder in the molten pool created at the coated surface, another way to coat substrate surface before the PTA treatment has been studied. As the powder can not be simply deposited on the substrate surface because of the plasma flow which would blow it off before melting it, a tape casting process was used to obtain an adherent powder layer on the material surface. Its cohesion and adhesion to the substrate are due to the organic binder contained in the tape to form organic bridges between particles. In this paper, the electrical properties of NiCu (70/30) tapes deposited on cast iron substrates were first studied. It has been shown that the binder led to a low electrical conductivity of the layer. PTA treatment of the casted tapes has been carried out by starting the electrical arc on the metallic cast iron substrates. The process control by CCD camera allowed to observe that the NiCu particles fell in the melting pool created at the substrate surface. The study of the obtained alloy compositions has shown the drastic influence of the initial binder concentration in the tape. Moreover, before being treated by PTA, some NiCu tapes were heated in a furnace at 1100°C for 4 hours to remove the organic binder and sinter the layer. The coatings thus produced, which were characterized by a low electrical resistivity and a good adhesion to the substrate, were then treated by PTA. The surfacing alloy properties were compared to those obtained without heat treatment.

Plasma transferred arc (PTA) allows to weld a metallic coating to a metal substrate in order to improve their wear and corrosion resistance. This process is mainly used for steel reclamation and the principal applications are coatings of valves, valve seats in automotive industry and extruder screws for plastic industry. This paper describes the tape casting of NiCu and NiCoCrAlTaY particles on Ni-based alloys and the various organic additives used in addition to a homogeneous metallic film. The initial results of treating these films with PTA regeneration are described. Paper includes a German-language abstract.

Aluminium alloys are extensively used materials which can be found in all kinds of industrial applications. They have distinctive advantages such as a high strength/weight ratio, an excellent workability and a good corrosion behaviour. However, aluminium alloys have wear resistance properties which limitate further use of these alloys. Plasma transferred arc surfacing (PTA) using the DCCP-technology (Direct Current Combined Polarity) was used for enhancing wear properties of different aluminium alloys (AlMgSi0.5, AlSi12) by the formation of an alloyed layer with added ceramics. Hardness of the base material could be increased by more than two times while the wear resistance of the modified aluminium alloy was about ten times higher compared to the base material. Paper text in German.

Alloying of the melt with nitrogen in order to improve material properties is well known in steel-making. This effect can also be used in plasma-powder-welding for a distinct improvement of corrosion- and wear-resistance. Using alloys comparable to material numbers 1.4016 and 1.4404 the influence of the process parameters in plasma-powder-welding on the proportion of nitrogen in the cladding is shown. In addition recommendations are made for the regulation of nitrogen concentrations, that are located far above saturation concentration of the alloys mentioned above. With the recommended parameters it was for the first time achieved to succesfully produce claddings with a nitrogen percentage by weight of up to 0.85 at a partial pressure between 0.045 and 0.065 MPa that allow reproducibility. Paper text in German.