This work is concentrated on plasma sprayed cermet coatings consisting of stainless steel (SS) (17 wt % Cr and 12 wt % Ni) and chromium oxide (Cr 2 O 3 ). These powders were sprayed simultaneously, however being injected separately to account for the drastic difference in their thermo-physical properties. Chromium oxide was injected internally and stainless steel externally. The plasma parameters (arc current, hydrogen vol %, mass flow rate) were optimized as well as the injector positions. Coatings were achieved with different mass ratios of SS and Cr 2 O 3 . All exhibited a lamellar structure with well distributed Cr 2 O 3 and SS lamellae. They were then systematically characterized by their phase content (XRD), composition (EDS), Vickers micro hardness, morphology (SEM), slurry and dry wear resistances. Finally the best dry linear abrasion resistance was obtained for the pure chromium oxide coatings, while the best slurry wear resistance corresponded to coatings with a mass ratio SS/ Cr 2 O 3 of 56/44.

The general method of process maps to understand and control thermal spray processes has been applied to monitor the deposition of WC-Co by high velocity oxygen fuel (HVOF). A selected number of particle state conditions (velocity and temperature) has been performed to produce a variety of coatings. Microstructure, mechanical properties, and wear resistance were evaluated and compared. A second order process map for sliding wear, impacting particle erosion and abrasive wear control can be constructed from the process map to provide the limits within which the particle state can be changed to achieve a predefined coating specification. The mechanisms behind the wear resistance are discussed within the framework of wear maps –third order process map-in the context of analysis of inter splat de-bonding, mechanical properties of the coating, and delamination failure.

This paper presents the results of a study on arc-sprayed coatings made from powder-cored wire. The wires used consist of a ferrochromium core with additions of boron, aluminum, and carbon compacted in a steel sheath. The coatings are sprayed using a modified burner operated at 34 V and 140 A with an air jet pressure of 0.6 MPa. During spraying, specimens are rotated at a speed of 60 rpm. XRD analysis is used to examine the initial phase composition of the layers as well as friction-induced changes in the subsurface resulting from block-on-ring wear tests. Cross-sectional examination shows that the coatings have low porosity (∼10%) and small grain size (50 to 150 µm). Based on these findings, it is concluded that the wear resistance of wire arc sprayed coatings is largely determined by powder wire composition, initial coating structure, and the structural stability of the subsurface layer. Paper includes a German-language abstract.

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 aim of this study is to show how electron beam remelting affects the structure and properties of CoCrW coatings. As described in the paper, CoCrW powders are plasma sprayed onto nickel substrates and a modified electron beam welder is used to remelt the deposits. The effects of the treatment are assessed via SEM and XRD analysis, wear testing, and hardness measurements. In summary, electron beam remelting improves a number of coating properties including adhesion strength and fretting wear resistance. It also eliminates oxide inclusions and lamellar structures and reduces layer porosity. Paper includes a German-language abstract.

This paper examines WC based coatings with high-alloy binders with regard to their structure, corrosion behavior and wear. The coatings are compared to conventional coatings with respect to corrosion and wear. The coatings were made using HVOF spraying of various powders. All powders examined were produced by agglomeration/sintering, that is by agglomeration of metal particles with WC particles and subsequent sintering. Some powders have been made using pre-alloyed metal particles. The paper also examines a mixture of ceramic-metallic powder and purely metallic powder. Various methods are used to characterize the powders and coatings. Paper includes a German-language abstract.

In this paper, a simple cutting method is used to examine the changes in wear resistance of four thermally sprayed coatings, two yttrium stabilized zirconia, and two aluminum oxides using a heat treatment. These changes were correlated with the changes in the microstructure of the application layers, which were characterized using intrusion porosimetry, scanning electron microscopy, and small-angle neutron scattering. Analysis of the results shows that changes in wear resistance are believed to have been caused by changes in the shape and surface area of the voids caused by sintering as well as crystallographic phase changes. Paper includes a German-language abstract.

This paper compares three thermally sprayed coatings with different carbide types in a NiCr matrix (25% by volume) with regard to their erosion, corrosion, and wear resistance. The three types of carbide are WC, chromium carbide, and TiC. The coatings were sprayed with the Sultzer-Metco Diamond-Jet 2600 equipment. All coatings were produced with the same spray parameters. If the sand particles hit the surface at high angles of impact, the WC coating is better than the other two coatings in terms of erosion/corrosion resistance. Micro-abrasive wear tests also showed the WC coating was superior (slightly better than the TiC coating). The corrosion properties of the coatings were almost the same. Paper includes a German-language abstract.

This paper describes investigation into the effect of the inorganic fillers on structural and physical-mechanical properties of polyethylene-based composite coatings produced by thermal spraying. A comparative analysis of the thermal spraying methods was carried out using spray polymers as an example. It was found that the powder particles made of aluminum and an Fe-B alloy, which were added to the polymeric materials, act as artificial crosslinking centers. This resulted in a decreasing grain size and an improvement in the physical and mechanical properties of the coatings. At low fill levels of the polymeric materials (up to 10% by volume), the degree of oxidation of the coating material decreased during spraying. Paper includes a German-language abstract.

This paper reviews the results of thermal spraying on the magnesium alloy AZ 91. By plasma, arc and HVOF spraying various metal based alloys were used as coating materials. The layers were investigated with regard to microstructure, bonding and corrosion resistance. Paper text in German.

This paper investigates the wear resistance of NiCr-Fe+50(80)%chromium carbide and NiCr-Fe+50%SiC coatings. This is achieved by the plasma spraying of composite powders and the mechanical mixing of powders, followed by an additional treatment with pulses of a plasma jet. The mechanism of wear of the sprayed coatings is also analyzed. Paper includes a German-language abstract.

The wear resistance of thermal spray coatings mainly depends on coating properties such as the microstructure, hardness, and porosity, as well as on the residual stress in the coating. The residual stress is induced by a variety of influences e.g. temperature gradients, difference of the thermal expansion coefficient of the coating / substrate materials, and the geometry of the components. To investigate the residual stress, the Impulse Excitation Technique was employed to measure the Young’s and shear moduli. The residual stress was determined by using the hole-drilling method and X-ray diffraction. Pin-on-Disc and Pin-on-Tube tests were used to investigate the wear behavior. After the wear tests, the wear volume was measured by means of a 3D-profilometer. The results show that the value of the residual stress can be modified by varying the coating thickness and the substrate geometry. The compressive stress in the HVOF-sprayed WC-Co coatings has a significant positive influence on the wear resistance whereas the tensile stress has a negative effect.

A ball-milled mixture of glass and alumina powders has been plasma sprayed to produce alumina-glass composite coatings. The coatings have the unique advantage of a melted ceramic secondary phase parallel to the surface in an aligned platelet composite structure. The alumina raises the hardness from 300HV for pure glass coatings to 900HV for a 60wt% alumina-glass composite coating. The scratch resistance increases by a factor of three and the wear resistance by a factor of five. The glass wears by the formation and intersection of cracks. The alumina wears by fine abrasion and supports most of the sliding load. The wear resistance reached a plateau at 40-50vol% alumina, which corresponds to the changeover from a glass to a ceramic matrix. Keywords: glass composite coatings, wear, thermal spraying

Borides are promising materials with good wear and corrosion resistance properties. Boride coatings are expected to perform better where wear and corrosion resistances are simultaneously required. Zirconium diboride is an important emerging material for such applications, due to its high hardness, high melting point, good wear resistance and corrosion as well as high temperature oxidation resistance. Special properties of laser beam like beam directionality, high intensity and spatial resolution makes laser alloying a fast and efficient technique for producing improved wear resistance coatings. In the present work, mild steel was laser alloyed with ZrB2, using "two-stage" technique of laser alloying. These coatings after characterization by optical microscopy, SEM, EDAX and XRD techniques were tested on a "Pin-on-Disk" machine for determining their wear resistance.

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

This paper presents a comparative study of the microstructure, phase properties, hardness, and wear resistance of high-pressure HVOF sprayed coatings. The layers were produced by the JP-5000 method using WC12Co and WC17Co powders varying in size distribution and morphology. Spray parameters were statistically evaluated using a design-of-experiments approach in order to optimize wear resistance as well as deposition efficiency, carbide grain size, and degree of oxidation. Paper includes a German-language abstract.

Aluminum coatings reinforced with either Al 2 O 3 or SiC particles were deposited onto aluminum substrates and subjected to various tests. The coatings were made with mechanically alloyed powders via atmospheric plasma spraying (APS). Both types of coatings had uniformly distributed hard particles, porosities in the range of 4 to 5%, and bond strengths of around 20 MPa. The wear resistance of the SiC-reinforced coatings, however, was almost 35% higher than the coatings containing Al 2 O 3 . X-ray examination (XRD) showed that the Al 2 O 3 particles undergo partial phase transformation during spraying, making them more prone to wear.

Exposed to particle erosion environments, metal-sprayed coatings are damaged by micro-machining and ploughing at low impact angles. The generation and propagation of subsurface lateral cracks at high impacting angles damage single-phase ceramic coatings. Therefore, multicomponent coatings deposited by high-energy processes have been widely used to provide wear protection in most of the applications. As commercial arc-sprayed coatings have been used to a limited extent in applications involving erosion and abrasion wear, developing attractive wear resistant arc-sprayed coatings has been found necessary. A cored wire formulation, referred to as Alpha-1800, has been developed to produce tailored arc-sprayed coatings that are tough enough to resist particle impacts at 90° and sufficiently hard to deflect eroding particles at low impact angles. Typical 1 mm-thick coatings composed of ductile and hard phases with Knoop hardness reaching 1800 kg/mm2 were easily produced by arc spraying the cored wire with air. Coatings were: 1) erosion tested at 25°C and higher temperatures at impact angles of 25° and 90° in a gas-blast erosion rig, 2) slurry erosion tested at impact angles of 25° and 90°, 3) abrasion wear tested using the ASTM G-65 test procedure. Results show that coatings produced with the new cored wire are at least 5 times more erosion resistant and 10 times more abrasion resistant than coatings produced by arc spraying commercial cored wires. The performance of the new arc-sprayed coating can be compared with that of high-energy WC-based coatings. Being thermally stable up to 850°C, arc-sprayed coatings produced with the new cored wire are attractive for applications in many industrial sectors up to high temperatures.

The cermet materials have been developed to protect surfaces against wear and corrosion. In cutting tools technology as well as chromium replacement, WC coatings have been used to improve life and performance at higher temperatures. This work compares the abrasion and adhesion resistance of a WC-Co mixed in a x:y relation with a NiCrBSiW alloy deposited by High Velocity Oxy-Fuel (HVOF) process using a JP-5000 gun in two conditions: as sprayed and thermally treated. Abrasion and adhesion tests were performed according to ASTM G-65 and ASTM C-633 respectively. The microstructure and composition of the coatings, failure and worn surface were evaluated using Optical (OM) and Scanning Electron Microscopy (SEM) as well as X-Ray energy Dispersive Spectroscopy (EDX) and X-Ray diffraction (XRD). Vickers microhardness under a 500g load has been averaged from 8 indentations per sample. The results showed that the coatings studied presented a similar microhardness as well as good abrasion resistance. The best behavior of the post-heated coating could be attributed to a lower porosity, better distributions and effective cohesion between hard phases. Partial recrystallization of the amorphous phase produced during the thermal spray process into sub-carbides could be related to the improvement in abrasion resistance of the post-treated coating.

This paper gives an account of pin-on-disc low stress abrasive wear and erosion wear tests on the specimens made by oxy-acetylene flame spray-fusing technology to explores the effect of WC content on the wear resistance of oxy-acetylene flame spray-fusing overlays. In the test, Ni60, NiWC25 and NiWC35 three kinds of various WC content Ni-base self-fluxing alloys were used as the typical wear resistance materials compared with 16Mn material and high Cr cast iron arc surfacing overlay. In pin-on-disc wear tests, SiC, Al 2 O 3 and SiO 2 different abrasive were used, and in erosion wear tests 30° and 90° erosion wear tests were performed. This paper also analyzed the wear mechanisms of spray-fusing overlays that possess different WC content by means of hardness tests and overlay's structure analysis. The results show that WC content influences the wear resistance of spray-fusing overlays greatly, but in various wear type and conditions, its effect's degree and tendency are quite different.