This study shows how data-driven modeling tools aid in the development of alloys that meet specific processing, property, and performance requirements. By leveraging a “big data” approach, two new alloys were designed that outperform commonly used materials in hardfacing and wear plate overlay applications. Over one million alloy compositions were analyzed to find two with the right combination of matrix and hard phases to provide the desired level of impact and abrasion resistance. The difference between the two alloys is in their matrix phase; one being austenitic, which has higher toughness, the other being martensitic, which has higher resistance to abrasive wear.

In this study, different air-cap configurations and shroud designs are developed and tested in twin wire arc spraying (TWAS) trails with the intent of increasing the collision probability of in-flight particles and thereby controlling coating composition and microstructure. In order to obtain greater insight on alloying effects and a better understanding of the coating build-up process, solid nickel and solid iron wires are used as feedstock materials and simultaneously sprayed on medium carbon steel substrates. The effect of polarity reversal and the use of a secondary atomization gas are also assessed. Detailed test results are presented in the paper along with in-depth analysis.

In this study, FeCrB coatings are deposited by wire arc spraying using powder cored wires to investigate the factors that affect thermal conductivity. Experimental results show that increasing boron content in the wires reduces oxide content in the coatings, which increases thermal conductivity. Annealing also increases thermal conductivity, which can be explained by grain growth and a reduction in porosity.

This study evaluates the friction and wear behavior of iron-base coatings produced by arc spraying using experimental cored wires. Coating microstructure was analyzed and various wear tests were performed. The results show that the tribological properties of the ferrous coating materials are greatly affected by porosity, oxide inclusions, particle shape, and microhardness.

Zn, Zn-Al and Zn-Mg coatings have been produced by cold spraying. By careful tuning alloy compositions and spray conditions, dense coatings are produced with a hardness of 200 HV0.01 that are up to four times harder than pure bulk Zn, thus meeting the requirements for print applications. These new developments open opportunities for producing harder and more wear resistant coatings, which may allow for the production of larger number of copies without compromising quality.

During solidification, the cooling behaviour of materials depends on the heat flow through the mould and the alloy composition. Even though the alloy composition is same; the cooling rate can change the properties of the materials. In the present study, an attempt has been taken to predict the cooling behaviour of gray cast iron into a resin bonded sand mould at various thicknesses using JL FEM analyser software. Using K-type thermocouple, the temperature was measured after every 20 sec. Both, the computer simulated and experimentally investigated cooling curves show the similar nature or pattern of the curves. The microstructure also confirms that the cooling rate changes the structure of the cast iron from gray to white.

Nickel-based superalloys can be used at temperatures up to 1050 °C in air. Superalloy open cell foam sheets with skin layers plasma sprayed on both sides can be used as high temperature heat exchangers provided that the two deposited skins are dense and well adhered to the open cell foam. In this study alloy 625 skins were deposited on each side of a sheet of metal foam by APS and HVOF to form a sandwich structure. Two densities of open cell foams, 20 and 10 pores per linear inch (ppi), were used in this study as the core. The initial Ni foam was converted to an alloy composition by plasma spraying aluminum and chromium on the foam’s struts with subsequent diffusion/solutionizing heat treatments before the alloy 625 skins were deposited. The microstructure of the coatings and the interface between the struts and skins was investigated. A layer of Ni-Al alloy was formed near the surface of the struts as a result of the heat treatment. The foam struts were imbedded more deeply into the coatings deposited by HVOF than the coatings deposited by APS.

Atmospheric plasma spraying of alloys often results in their composition changes. The main source of the changes is usually preferential oxidation of some elements composing the alloy. As a rule, these are the alloying elements whose affinity to oxygen is high. Changes due to this effect are well known from metallurgy; however, they were scarcely studied from the point of view of plasma spraying. Preferential evaporation of some elements may also contribute to the alloy composition changes. The aim of the present paper is to give quantitative data on composition changes of selected alloys sprayed by a water-stabilized plasma gun. Two Ni-base alloys and one high-alloy Cr-Ni-steel were studied. The main tool for determining the sample composition was electron probe X-ray microanalysis. To quantify the results and to eliminate the systematic errors, the data obtained by this method were calibrated by repeated chemical analysis of feedstock powders. The alloy composition was determined after both stages of plasma spraying, i.e. after the inflight stage of molten particles and after the stage comprising particle impact, solidification, coating formation and cooling. To study the situation after the former stage, the flying particles were trapped and quenched in liquid nitrogen. In the Ni-Cr alloy containing 20%Cr, strong Cr depletion was observed. The Fe depletion in the Ni-Fe alloy (47%Fe), though unambiguous, was less significant. The high-alloy steel (Czech equivalent of AISI 316) was also Cr depleted, whereas the concentrations of other alloying elements (Mo, Ni) remained effectively unchanged. In all cases, the depletion occurred at the first spraying stage and became more pronounced during the second stage. Strong air entrainment occurs not only in a plasma jet produced by a water-stabilized plasma gun, but also if gas-stabilized plasma guns are used in atmospheric plasma spraying. It follows that the dominant mechanisms of composition changes during plasma spraying by both techniques are similar.

Chemical reactions between melted materials and their gaseous environment are generally inherent to the thermal spray process. Measures to promote and control these reactions are the distinguishing characteristic of reactive plasma spraying. In this paper, Ti-6Al-4V nitrided coatings are produced by high-pressure reactive plasma spraying. The coatings are deposited at different pressures up to 250 kPa in a reactive nitrogen atmosphere as well as air in order to study the influence of spraying pressure and atmosphere. The microstructure and phase composition of the Ti-6Al-4V layers are examined with the aid of X-ray analysis, microprobe measurements, and electron imaging. The investigations show that the pressure-supported nitrogen application during spraying led to the formation of fine and coarse TiN in the Ti matrix. Paper includes a German-language abstract.

This work investigates the effect of processing parameters on the microstructure and composition of Ni-base alloys produced by laser forming, an additive technique also known as direct metal deposition. The parameters assessed in the study include powder flow rate, traverse speed, laser power, and spot size. In all experiments, a melt pool diameter of 0.3 mm was maintained. The results show that laser formed alloys are similar in structure to conventional wrought alloys with additional peaks formed as a result of the oxidation of active alloying elements. The complex compounds observed on the surface of the laser formed samples disappeared after polishing. Paper includes a German-language abstract.

Cored wires expand the spectrum of coating materials, that can be processed from wire feedstock. In particular they allow to provide a custom-made alloy composition. For many industrial applications a low thermal expansion coefficient is desirable to adapt the expansion behavior to specific needs. Bulk material alloys within the system Fe-Ni-Co show thermal expansion coefficients below 5 10 –6 K –1 at temperatures below 600 °C. Thermal spraying is a suitable technology to manufacture coatings, that provide a gradient of the thermal expansion behavior, or free standing bodies for components with low shape changes due to thermal interference. Detailed research has to be done on the influence of the alloy composition regarding the specific metallurgical requirements on wire feedstock material for arc spraying. Fe-Ni(-Co) coatings are produced from cored wires by arc spraying. Guidelines for the choice of the optimum process parameters with respect to coating properties and economical effects are worked out. The coatings are characterized with concern to porosity, oxide content, surface roughness, deposition efficiency, power consumption and deposition rate. The coefficient of thermal expansion is determined by dilatometry.

Amorphization induced by sliding wear and consequent wear resistance have been investigated in relation with the microstructure of Fe-Cr-B alloy spray coatings. The Fe-Cr-B spray coated layer exhibited much higher wear resistance and significantly lower friction coefficient in comparison with that of low carbon steel substrate thanks to the amorphous surface film formed during the dry sliding wear. Electron microscopy on the cross-section of the coated layer exhibited intra-particle segregation associated with rod-shape Cr rich (Cr,Fe)xB particles in the matrix of Fe-Cr solid solution phase. From the observations using TEM and EDS, Fe-Cr solid solution phase with super-saturated B and Si content was confirmed to be the phase which mainly contribute to the crystalline-to-amorphous transition induced by sliding wear. The formation of oxide inclusions seems to impede the crystalline-to-amorphous transition by lowering the solute content in Fe-Cr solid solution phase. Keywords : microstructure, wear-resistance, Fe-Cr-B alloy, amorphization, detonation gun

WC-Co and WC-CoCr coatings were deposited with the JP-5000 liquid fuel HP/HVOF system using various thermal spray powder types. The microstructure, microhardness, deposition rate and wear resistance of the coatings were characterized. The results show that these coatings provide significantly more protection from dry three-body abrasion than from dry sand erosion, when compared to mild steel. They also provide more advantage at low angles of erosion than at high angles of erosion. Furthermore, the coating composition was found to have a significant effect on the wear rates, with WC-CoCr providing the best wear resistance even after taking the higher cost of the powder into account. The powder manufacturing route had only a secondary effect on the wear rates, except in the case of fused and crushed powder, which produced an inferior coating.

For the purpose of getting high hardness and high wear-resistant coating by arc spraying technology, the arc spraying of 7Cr13 cored wire is adopted in this paper. The metallurgical process of the cored wire arc spraying is discussed. The bond strength, hardness and tribological properties of the composite coating are investigated.

Molybdenum based thermal spray coatings are used extensively for wear and friction control. However, the sprayed Mo lamellae have been found to have low breakout resistance leading to decreased wear life of these coatings. An alternate approach is to increase the strength of Mo lamellae by alloying them with Mo-C. This work examines the effect of such alloying on the differences in the friction and wear mechanisms of four Mo and Mo-Mo-C based coatings. It was found that alloying the Mo with Mo-C leads to an improvement in the friction behavior of Mo-Mo-C based coatings.

This paper describes variations in the microstructure/composition and mechanical properties in plasma sprayed CoCrAlY coatings and a modified Rene 80 substrate of gas turbine blades operated for 21000 h under liquefied natural gas fuels. Substantial oxidation/carbonization occurred in near surface coatings of concave blades but not in convex coatings. Aluminum and nickel/titanium rich nitrides formed in concave coatings and substrates adjacent to the interface, respectively. Small punch (SP) specimens were prepared in order that the specimen surface would be located in the near surface and interface regions of the concave and convex coatings. In SP tests, brittle cracks in the near surface and interface coatings of the concave blade initiated at low strains up to 950 °C. The convex coatings had higher ductility than the concave coatings and substrate and showed a rapid increase in the ductility above 800 °C. Thus it is apparent that the oxidation/carbonization and nitridation in the concave coatings produced a significant loss of the ductility. The in-service degradation mechanism of the CoCrAlY coatings is discussed in light of the operating temperature distribution and compared to that of CoNiCrAlY coatings induced by grain boundary sulfidation/oxidation.

In corrosive media the wear resistance of ceramic-metallic coatings is dependent on the corrosion resistance of the metal matrix. Other factors that will affect the coating deterioration are the corrosivity of the medium and any galvanic interaction from the surrounding material. This paper presents results from a study where different types of WC(Co/Cr/Mo/Ni) powders have been sprayed by HVOF, Diamond Jet 2600 Hybrid equipment. The properties of the sprayed coatings have been verified by metallographic studies and by erosion-corrosion testing both under corrosive and non-corrosive conditions. The results clearly demonstrate the importance of having a metal matrix at least as corrosion resistance as the surrounding materials. When wear exposed components in pipe systems, pumps or valves are coated with a WC type coating, the corrosion resistance of the metal matrix should be compatible to the material of the rest of the system. This is especially important when the surrounding materials are corrosion resistant alloys as stainless steels, where the coatings otherwise will act as an anode.