Juha Lagerbom

Development of thermal spray powders for improved tribological and corrosive applications and cost-effective solutions

HVOF sprayed carbide/metal coatings are used widely to prevent wear and corrosion of engineering components. However, in some specific applications additional properties, such as low friction surfaces with good sliding properties and/or more improved corrosion resistances with simultaneous high wear resistance are required. Often such properties are not obtained by using conventional commercial spray powder compositions. The cost of the spray powders and sprayed coating plays very often also an important role. Therefore, cost-effective solutions are also needed. The aim of the present work is to describe the development of special hard metal powders with tailored powder compositions and structures. Experimental Cr3C2-25Ni + 10vol-% solid lubricant powders, WC-15% corrosion resistant metal binder powders, and WC-10Co-4Cr powder manufactured from recycled hard metal scrap were prepared by using the spray drying and sintering process. The powders were sprayed by High-Velocity Oxy-Fuel (HVOF) spray process. The microstructures of the developed powders and coatings are reported.

Alternative Fabrication Routes toward Oxide-Dispersion-Strengthened Steels and Model Alloys

The standard powder metallurgy (PM) route for the fabrication of oxide-dispersion-strengthened (ODS) steels involves gas atomization to produce a prealloyed powder, mechanical alloying (MA) with fine oxide powders, consolidation, and finally thermal/thermomechanical treatment (TMT). It is well established that ODS steels with superior property combinations, for example, creep and tensile strength, can be produced by this PM/MA route. However, the fabrication process is complex and expensive, and the fitness for scaling up to the industrial scale is limited. At the laboratory scale, production of small amounts of well-controlled model systems continues to be desirable for specific purposes, such as modeling-oriented experiments. Thus, from the laboratory to industrial application, there is growing interest in complementary or alternative fabrication routes for ODS steels and related model systems, which offer a different balance of cost, convenience, properties, and scalability. This article reviews the state of the art in ODS alloy fabrication and identifies promising new routes toward ODS steels. The PM/AM route for the fabrication of ODS steels is also described, as it is the current default process. Hybrid routes that comprise aspects of both the PM route and more radical liquid metal (LM) routes are suggested to be promising approaches for larger volumes and higher throughput of fabricated material. Although similar uniformity and refinement of the critical nanometer-sized oxide particles has not yet been demonstrated, ongoing innovations in the LM route are described, along with recent encouraging preliminary results for both extrinsic nano-oxide additions and intrinsic nano-oxide formation in variants of the LM route. Finally, physicochemical methods such as ion beam synthesis are shown to offer interesting perspectives for the fabrication of model systems. As well as literature sources, examples of progress in the authors’ groups are also highlighted.

Material Challenges in the Manufacturing of Tailored Structures with Direct Write Technologies

Two different direct write technologies, Direct Write Paste (DWP) and Direct Write Thermal Spray (DWTS), and the general material challenges related to these technologies are described in this paper. These new technologies open new routes to produce highly functional products that can be tailored and customised according to the demands of the applications. The DWP process is based on dispensing paste-like materials through a tip onto a substrate. Depending on the paste material, either 2 or 3 dimensional structures can be printed. The DWTS technique is based on thermal spraying, which is a spray process where the powder material is accelerated in molten form and impinged onto a surface. Products made using DWTS are especially targeted at harsh environment solutions. Results related to development of printable materials and printed products are presented.