Gas-Shielded Tungsten Arc Welding (GTAW) was modified to a Flux-Cored-Double-Wire GTAW (FCDW-GTAW); in this technique, wires of different compositions are used simultaneously to obtain different microstructures. In the modified GTAW, automatic flux-cored double-wire was used with a combination of four different wires deposited in AISI1020 steel, allowing different microstructures. Pin-on-disk wear tests described by ASTM G99 was used to evaluate the wear coefficients of four hardfacing materials combining Fe–Cr–C, Fe-Cr-C-Nb, Fe-Cr-C-Mo-Nb, and Fe-Cr-C-Mo-Ti alloys. The combination of these wires resulted in a hypoeutectic microstructure with niobium and titanium carbides, with an average hardness of 650 HV0.3, and hypereutectic microstructures formed by different niobium contents, with a microhardness range from 820 to 1020 HV0.3. The wear tests were performed without lubrication at room temperature, using a 6.0 mm diameter polished alumina sphere as a counter-body. The total distance covered was 1000 m with a speed of 0.1 m/s, a track radius of 6.0 cm, and an applied load of 10 N. Hardness, microstructure, wear coefficient, and wear mechanisms were compared. The results showed that wear resistance could be differentiated by the predominant wear mechanism: polishing for the hypoeutectic hardfacing and cracking for the hypereutectic ones.

Resumo Esta revisão apresenta possíveis estratégias para aumentar a resistência ao desgaste de revestimentos duros, baseado no projeto conjunto de matriz metálica e segunda fase dura. Como a resistência ao desgaste não é uma propriedade intrínseca do material, os resultados de vários ensaios de desgaste são discutidos à luz da interação entre propriedades mecânicas e severidade de desgaste, o que é dependente da microestrutura. Estas estratégias são baseadas no aumento de dureza, considerando o tipo e tamanho da segunda fase dura; a tenacidade à fratura e o nível de diluição do revestimento. As diretrizes fornecidas para o melhor projeto de ligas de revestimentos duros para condições usuais de abrasão dependem da fração volumétrica de segunda fase dura.

Abstract This review presents the possible strategies to increase the wear resistance of hardfacing alloys based on metallic matrix and second hard phase’s coupled design. As the wear resistance is not an intrinsic property of material, the results of many wear tests are discussed in light of the interaction between mechanical properties and wear severity, which is dependent on the microstructure. These strategies are based on the hardness increase, considering the kind and size of the second hard phase, the fracture toughness, and the dilution level of hardfacing. The guidelines provided for designing better the hardfacing alloys for usual abrasion conditions depending on the volume fraction of the second hard phase.

ABSTRACT The hardfacing deposition with the GTAW process is widely studied with the addition of metallic powder or solid wire. This study introduces an original method, flux-cored-double-wire GTAW (FCDW-GTAW), where wires of different compositions are used simultaneously to deposit hardfacing. Because of the complexity in stabilizing the welding system, the combined effects of welding parameters should be investigated, allowing elaborate prediction models for the geometry and dilution of the deposits. These aspects are crucial for the target application, wear-resistant layers based on Fe-Cr-C composition, requiring a low-level of dilution and bead-geometry quality. Five parameters were chosen to model the deposition: the welding current, welding speed, standoff distance, torch angle, and wire feed pulse frequency. Therefore, using Response Surface Methodology with five factors at five levels to plan the experiments, thirty-two deposition conditions were necessary to model responses. Complete and reduced models were presented for width, reinforcement, penetration, and dilution responses. The reduced models showed a better prediction than the complete ones. The welding parameters’ interaction was identified for the reduced models, where the welding current and speed were influential in all responses. Results showed the possibility of obtaining good quality in the beads applying the FCDW-GTAW technique.

Abstract The use of a gouging abrasion test to evaluate the wear of jaw crushers is revised in terms of its procedures, considering the effects of the most significant variables, such as the minimum amount of crushed material and the minimum opening between the jaws during the crushing cycle (minimum discharge aperture). A correlation between the work hardening of jaws and the amount of crushed material is presented. The wear of stationary and movable jaws is compared, being the results dependent on the jaw's material and the discharge aperture. The abrasiveness of several rocks was evaluated, showing a good correlation with their Mohs hardness.

Indentation morphologies depend on the mechanical properties of materials, especially the strain-hardening exponent and yield strength-to-elastic modulus ratio. Hernot et al.¹ described a model that can be used to obtain the indentation morphology index from properties determined in tensile tests. The model is used here with two aluminum alloys and 1020 steel tested under spherical indentation with different loads and ball diameters. There was good agreement between the values predicted by the model and the experimental findings for all the materials tested except partially recovered AA1350 aluminum alloy (H24 condition). This exception is discussed and a possible explanation for it is sought in other experimental deviations and in microstructural inhomogeneities.

Surface tailoring with plasma transferred arc (PTA) hardfacing involves the deposition of powder mixtures to produce coatings with an almost unlimited chemical composition. PTA hardfacing is particularly important for processing low weldability alloys, such as those for high-temperature applications, of which NiCrAlC is an example. This study analyzed NiCrAlC coatings processed by PTA using a mixture of elemental powders. Deposition on AISI316L plates was carried out with currents of 100 A and 130 A to induce variations in the chemical composition of the coatings, which were also subjected to isothermal exposure at temperatures of up to 1000 ºC for up to 72 hours in an air furnace. The results show that the aluminide compounds were stable, the coatings that solidified more slowly having the highest hardness after temperature exposure and potentially being suitable for use in high-temperature abrasion environments.

This paper presents subsurface hardening results of the low-carbon steel plate, deformed under industrial test conditions by punches manufactured in quenched and tempered AISI D2 steel, with and without TiN coating. The punches are 12º double shear angle shaped. A longer tool life was obtained in tools with TiN coatings applied by Physical Vapor Deposition (PVD) process. The depth of hardened layer generated through punching was different for the work piece and slug. In the workpieces, this layer was about 1.5 mm wide, whereas in the slugs no hardness stabilization values were observed up to 4 mm. Moreover, the presence of the TiN coating did not affect the subsurface hardening produced by punching. The results were discussed regarding the wear mechanisms and the role of TiN coating at the interface. Therefore, the thermal effects were not relevant during the punching tests.