Effect of Tungsten Carbide Morphology, Quantity, and Microstructure on Wear of a Hardfacing Layer Manufactured by Plasma Transferred Arc Welding

Hardfacing layers on mild steel substrates were successfully manufactured using a plasma transferred arc welding (PTAW) process to combine tungsten carbide powder and binder metal. Three morphological types of tungsten carbide powder were employed: spherical, fused angular, and mixed powder. The effects of both the morphology and the quantity of tungsten carbide powder on the wear property of the products were determined using a dry sand wheel abrasion test. The results revealed that two conditions effectively increased the wear resistance of the hardfacing layers: the use of spherical tungsten carbide and the use of an increased quantity of tungsten carbide. Moreover, the formation of an interfacial layer of intermetallic compounds (IMCs) between the tungsten carbide and binder metal, and the relationship between the microstructure of the IMC layer and its wear property were also investigated. It was confirmed that, in general, preferential wear occurs in the binder metal region. It was also unveiled that the wear property improves when interfacial IMC bands are formed and grown to appropriate width. To obtain a sound layer more resistant to wear, the PTAW conditions should be adequately controlled. In particular, these include the process peak temperature and the cooling rate, which affect the formation of the microstructure.

Matrix Composite Coatings Deposited on AISI 4715 Steel by Powder Plasma-Transferred Arc Welding. Part 3. Comparison of the Brittle Fracture Resistance of Wear-Resistant Composite Layers Surfaced Using the PPTAW Method

This article is the last of a series of publications included in the MDPI special edition entitled “Innovative Technologies and Materials for the Production of Mechanical, Thermal and Corrosion Wear-Resistant Surface Layers and Coatings”. Powder plasma-transferred arc welding (PPTAW) was used to surface metal matrix composite (MMC) layers using a mixture of cobalt (Co3) and nickel (Ni3) alloy powders. These powders contained different proportions and types of hard reinforcing phases in the form of ceramic carbides (TiC and WC-W2C), titanium diboride (TiB2), and of tungsten-coated synthetic polycrystalline diamond (PD-W). The resistance of the composite layers to cracking under the influence of dynamic loading was determined using Charpy hammer impact tests. The results showed that the various interactions between the ceramic particles and the metal matrix significantly affected the formation process and porosity of the composite surfacing welds on the AISI 4715 low-alloy structural steel substrate. They also affected the distribution and proportion of reinforcing-phase particles in the matrix. The size, shape, and type of the ceramic reinforcement particles and the surfacing weld density significantly impacted the brittleness of the padded MMC layer. The fracture toughness increased upon decreasing the particle size of the hard reinforcing phase in the nickel alloy matrix and upon increasing the composite density. The calculated mean critical stress intensity factor KIc of the steel samples with deposited layers of cobalt alloy reinforced with TiC and PD-W particles was 4.3 MPa⋅m12 higher than that of the nickel alloy reinforced with TiC and WC-W2C particles.

Microstructure and Abrasive Wear Resistance of Metal Matrix Composite Coatings Deposited on Steel Grade AISI 4715 by Powder Plasma Transferred Arc Welding Part 1. Mechanical and Structural Properties of a Cobalt-Based Alloy Surface Layer Reinforced with Particles of Titanium Carbide and Synthetic Metal–Diamond Composite

The article discusses test results concerning an innovative surface layer obtained using the cladding with powder plasma transferred arc welding (PPTAW) method. The above-named layer, being a metal matrix composite (MCM), is characterised by high abrasive wear resistance, resistance to pressure and impact loads, and the possibility of operation at elevated temperatures. The layer was made using powder in the form of a cobalt alloy-based composite reinforced with monocarbide TiC particles and superhard spherical particles of synthetic metal–diamond composite provided with tungsten coating. The surface layer was deposited on a sheet made of low-alloy structural steel grade AISI 4715. The layer is intended for surfaces of inserts of drilling tools used in the extraction industry. The results showed the lack of the thermal and structural decomposition of the hard layer reinforcing the matrix during the cladding process, its very high resistance to metal-mineral abrasive wear and its resistance to moderate impact loads. The abrasive wear resistance of the deposited layer with particles of TiC and synthetic metal–diamond composite was about than 140 times higher than the abrasive wear resistance of abrasion resistant heat-treated steel having a nominal hardness of 400 HBW. The use of diamond as a metal matrix reinforcement in order to increase the abrasive resistance of the PPTAW overlay layer is a new and innovative area of inquiry. There is no information related to tests concerning metal matrix surface layers reinforced with synthetic metal–diamond composite and obtained using PPTAW method.

Theoretical evaluation of abrasive wear behavior of B4C/ FeCrC coating layer evaluated by a Taguchi approach

In this study, B4C and FeCrC powders were alloyed on the surface of AISI 430 by a fusion process via plasma transferred arc welding. Mixtures of these powders at various amounts were used. The microstructure and wear behavior of the obtained coating layers were investigated. The wear behavior of the coating layers was planned using the Taguchi method. Abrasive wear mass loss results were optimized with the “smaller the better” control characteristic of the Taguchi method, and the results were analyzed graphically. The actual data obtained at the end of the study were formed by using an L16 (4 × 2, 2 × 2) mixed array, and the remaining wear rates were calculated with the help of theoretical formulas in order to obtain theoretical abrasive wear results.

Microstructure Features and High Temperature Oxidation Resistance of In-Situ TiN-Ti Composite Coatings by Plasma Transferred Arc Welding

In order to improve the high temperature oxidation resistance of Ti6Al4V alloy, the in-situ TiN-Ti composite coatings were prepared with Ti-Cr-Ni-Nb powders by plasma transferred arc welding. Nitrogen gas was used as the transport gas and provided N source for the formation reaction of TiN. Microstructure features and high temperature oxidation behaviors of the composite coatings were studied. The phases in the composite coatings were TiN, Ti, CrN, and NiTi. It was clearly observed that in-situ TiN particles were evenly distributed in the Ti matrix. A little Nb atom dissolved in TiN particles, and others dissolved in the Ti matrix. By comparing the curve of Ti6Al4V alloy to that of the composite coatings, the oxidation mass gain of the composite coatings was comparatively less. The oxidation film of the composite coatings was smooth and compact, and no crack was visibly observed. Based on the results of the high temperature tests, the composite coatings exhibited superior high temperature oxidation resistance than Ti6Al4V alloy both at 650 °C and at 850 °C.

Microstructural Evolution and Mechanical Properties of Hybrid Bevel Gears Manufactured by Tailored Forming

The production of multi-metal bulk components requires suitable manufacturing technologies. On the example of hybrid bevel gears featuring two different steels at the outer surface and on the inside, the applicability of the novel manufacturing technology of Tailored Forming was investigated. In a first processing step, a semi-finished compound was manufactured by cladding a substrate using a plasma transferred arc welding or a laser hotwire process. The resulting semi-finished workpieces with a metallurgical bond were subsequently near-net shape forged to bevel gears. Using the residual heat after the forging process, a process-integrated heat treatment was carried out directly after forming. For the investigations, the material combinations of 41Cr4 with C22.8 (AISI 5140/AISI 1022M) and X45CrSi9-3 with C22.8 (AISI HNV3/AISI 1022M) were applied. To reveal the influence of the single processing steps on the resulting interface, metallographic examinations, hardness measurements and micro tensile tests were carried out after cladding, forging and process-integrated heat treatment. Due to forging and heat-treatment, recrystallization and grain refinement at the interface and an increase in both, hardness and tensile strength, were observed.

Effect of Nb Content on the Microstructure and Wear Resistance of Fe-12Cr-xNb-4C Coatings Prepared by Plasma-Transferred Arc Welding

The Fe-Cr-C coatings with different levels of Nb addition were prepared on carbon steel by a plasma transferred arc (PTA) weld-surfacing process and their microstructure and properties were investigated. As the Nb content increases from 8.96% to 12.55%, the coating gradually changes from a hypereutectic structure (martensite, austenite matrix, primary NbC and eutectic γ+M7C3) to a near eutectic structure (γ+M7C3 and NbC) and finally a hypoeutectic structure (primary γ, γ+M7C3 and NbC). As the Nb content increases, the hardness and wear resistance of the coating first increase and then decrease, which is closely related to the NbC volume fraction first increasing and then the NbC size coarsening. The Fe-Cr-C coating with 11.65% Nb balances the NbC content and size, and has the highest hardness and best wear resistance. As the Nb content increases further, the formation and aggregation of coarse NbC carbides in the coating results in high brittleness of the coating, which may cause the carbide particles to peel off the coating during the wear process, thereby reducing wear resistance.