Telmo Roberto Strohaecker

Effect of different surface states before plasma nitriding on properties and machining behavior of M2 high-speed steel

Abstract In the present work the effect of different surface conditions on the plasma nitriding response of AISI M2 high-speed steel was investigated. Samples and drills were prepared to different surface finishes prior to plasma nitriding: ground and sandblasted. Polished samples were used as a reference surface state. The plasma nitriding was performed at temperatures of 400 and 500 °C for two gas mixtures: 5 and 76 vol.% N2 in hydrogen. The surfaces were characterized before and after plasma nitriding concerning the microstructure, roughness, microhardness, chemical composition, phase composition and residual stress states. Machining tests were carried out with drills, during which drilling forces and flank wear were measured. A significant effect of the surface state prior to nitriding on the residual stress states and properties of the nitrided layer and untreated core has been observed. Thinner nitrided layers on ground and sandblasted samples were attributed to high compressive residual stress states and a stress-affected diffusion of nitrogen and carbon. In the machining tests, sandblasted drills exhibited the best performance. Lower nitrogen concentrations in the gas atmosphere gave the lowest drill flank wear for sandblasted surfaces, while higher nitrogen concentrations led to a reduction in drilling forces and torque.

Preliminary study on the mechanical behavior of friction spot welds

O processo de Soldagem a Ponto por Friccao (FSpW - Friction Spot Welding) caracteriza-se por possibilitar a uniao no estado solido de duas ou mais chapas de material sobrepostas sem deixar o furo residual caracteristico do processo FSW. O presente trabalho apresenta os primeiros resultados de estudos visando determinar a resistencia mecânica de juntas em ligas de aluminio soldadas por FSpW. Recentemente diversos estudos sobre o modelamento numerico de soldas realizadas por processos de soldagem baseados em friccao tem sido realizados, entretanto a maioria destes estudos esta relacionada a fisica do processo. Alguns trabalhos estabelecem a relacao entre as variaveis de processo e as propriedades mecânicas da junta resultante, mas e muito dificil encontrar na literatura resultados quantitativos que possam ser usados diretamente para projeto destas unioes. O presente trabalho objetiva desenvolver um processo de analise baseado nas caracteristicas do processo que permita avaliar como a geometria e microestrutura das regioes da solda afeta o comportamento mecânico das juntas resultantes. Com este objetivo, os resultados de ensaios mecânicos realizados em juntas de aluminio AA2024-T3 foram usados para validar e calibrar um modelo numerico desenvolvido para prever o modo de falha da uniao. O modelo numerico reproduz as dimensoes e carregamento utilizados nos ensaios de cisalhamento e tracao. As dimensoes e propriedades das regioes principais da junta (ZM - zona de mistura, ZTMA - zona termo-mecânicamente afetada, ZAC - zona afetada pelo calor e MB - metal base) foram definidas com base na medicao da dureza e analises macrograficas de corpos de prova soldados com diferentes parâmetros. Pode-se comprovar uma otima correlacao entre os resultados obtidos nas simulacoes e os dados experimentais. O modelamento numerico das juntas pernite a previsao das propriedades mecânicas da junta e auxilia na compreensao da influencia da geometria e propriedades de cada regiao sobre o seu desempenho em servico. Baseado nos resultados obtidos, o procedimento de analise pode ser facilmente adaptado para o processo de Soldagem a Ponto por Friccao e Mistura Mecânica (FSSW - Friction Stir Spot Welding).

Optimization of Friction Spot Welding Process Parameters for AA2198-T8 Sheets

The present work is aimed at the optimization of friction spot welding process parameters for 3.2 mm thick 2198-T8 aluminum alloy sheets; this was performed via a Taguchi-based analysis of the effect of process variables, namely rotation speed, welding time, and plunge depth, on the shear strength of the welded joints. In this study, low or intermediate rotation speed levels showed to be better for the process. Longer welding times and deeper plunge depths led to higher joint strength, although the influence of such parameters is found to be limited above certain values. Hardness profiles and fracture analysis were also performed.

Deposit by friction surfacing and its applications

This work will present the state of the art of deposition by means of the friction surfacing process, the influences of the deposition parameters and some applications of the process. In second part, some results for a study being conducted with deposition of three different consumable rods (materials for ABNT 8620, ABNT 4140, and AISI 310 steel rods) in a substrata of ABNT 1070 carbon steel will be presented, using as deposit parameters a rotational rod speed of 3500 rpm, traverse speeds of 8.5–17 mm/s, and axial pressure of 1.03 and 1.38 MPa. The deposits were characterized by visual analysis, macrograph analysis, micrograph analysis, micro hardness profile, and push-off test. The results so far were considered to be satisfactory, showing that the technique can be employed to repair surfaces of components in high carbon steels and for deposition of similar and dissimilar materials. However, the optimum parameters for the process must still be studied.

Microstructural and Mechanical Observations of Galvanized TRIP Steel after Friction Stir Spot Welding

Friction stir spot welding was done in transformation-induced plasticity steel sheets coated with zinc. The influence of tool rotational speed and dwell time on the microstructure and mechanical properties of lap-joints were investigated. After processing, different zones were formed in the joints. Microstructures in each zone depended on the welding conditions employed. Higher dwell time coupled with higher rotational speed promoted the deposition of a large amount of allotriomorphic ferrite beside the keyhole left by the pin. Coalesced bainite formation was stimulated by the deformation. Mechanical and chemical stabilization of the austenite occurred in different welding zones. Some zinc from the coating remained in the joint, in the stirring zone, representing a partial bonding between the steel sheets. The strength of the welds depended on a complex interaction between geometrical features, such as bonding ligament length and distance between the zinc and the keyhole left by the pin and the resultant microstructure in the stirring zone. The highest joint strength was observed for the “lowest tool rotational speed–highest dwell time” combination of welding parameters.

Thermally induced strains and total shrinkage of the polymethyl-methacrylate cement in simplified models of total hip arthroplasty

An evaluation of transient and stabilized strains in the cement mantle during polymerization was carried out in simplified cemented total hip arthroplasty (THA) model. A mathematical approach combined with a simple finite element simulation was used to compare measured and calculated stabilized strain values and to provide the Von Mises stresses at the stem/cement interface due to shrinkage related to temperature decrease after exothermal reaction. A second similar model was carried out to measure stem/cement/mold interfacial shear strength and dimensional changes of the cement mantle to obtain total shrinkage due to temperature decrease plus cement polymerization. The results indicated that positive strain peaks found during the exothermic stage of polymerization have the potential to produce pre-loading cracking. After the initial expansion, it was observed a progressive strain decrease pattern down to stabilized values that takes place near 2h after the cementation. Even though there is a great deal of dispersion in the measured stabilized strain values, in average those values match quite well with the numerical simulations, indicating 4,7 MPa von Mises interfacial stress due to thermal shrinkage. The total cement shrinkage leads to a negative radial stress of 11 MPa and 14 MPa von Mises interfacial stress. Finally, total shrinkage has the potential to enhance gaps in the cement/mold interface.

Duplex surface treatment of high strength Timetal 550 alloy towards high load-bearing capacity

In the present investigation, novel duplex systems combining nickel diffusion (ND) deep case hardening with low friction wear resistant TiN and diamond-like carbon (DLC) coatings have been designed and applied to high strength Timetal 550 titanium alloy. The load bearing capacity of the duplex treated Timetal 550 was assessed dynamically using both a scratch tester and an Amsler tribometer with a block-on-wheel configuration. Experimental results showed that the load bearing capacity of these low friction wear resistant coatings can be improved dramatically when deposited on ND-treated Timetal 550 substrate relative to material coated with TiN and DLC alone. It was also found that the DLC/ND duplex system possessed superior load bearing capacity to the TiN/ND duplex system.

Progress in friction stir welding of Ni alloys

ABSTRACT In recent years, interest has been increasing in application of Nickel alloys in the oil industry. For subsea engineering, the possibility to weld high-strength materials in an effective manner is essential. Friction Stir Welding (FSW) is alternative to join several materials retaining their properties or even improving them. This fact is relevant for Corrosion-Resistant Alloys (CRA) used in deep-water exploitation of hydrocarbons. Publications up to now have focused on FSW of Inconel® series as alloy 600, 625, and 718. To provide a solid basis for development, this review discusses the crucial points for FSW. The tool materials are described, as well as the joint microstructure and properties achieved. Furthermore, the basics of the corrosion resistance and the early corrosion studies of FSW joints are presented. It is concluded that FSW is a promising process for Ni alloys, but depends on upcoming research regarding tool technology and corrosion investigations.

Application of X-ray diffraction, micromagnetic and hole drilling methods for residual stress determination in a ball bearing steel ring

A basic understanding of distortion problems requires the analysis of a complete manufacturing process including an almost complete overview of residual stress states in the component during each production step. To reduce the measurement time in the future, three measurements methods (X-ray diffraction, micromagnetic and blind hole drilling methods) have been used to analyze residual stress states in machined AISI 52100 ball bearing rings. X-ray diffraction was used as a state-of-the-art method for machining induced residual stresses with pronounced gradients. The ring exhibited a complex residual stress state with high tensile residual stresses at the surface, a strong gradient in depth, and also showed some variation along the outer circumference due to a superimposition of machining induced residual stresses and effects from the clamping device process. Due to this surface state, micromagnetic signals depend on the analyzing frequency. A calibration of the signals was only possible with the X-ray diffraction data. The results of the three different measurement methods correlate reasonably well.

Friction Stir Welding of Precipitate Hardenable Aluminium Alloys: A Review

The precipitation hardenable 2xxx (Al-Cu), 6xxx (Al-Mg-Si) and 7xxx (Al-Zn) aluminium alloys considered before as “unweldable” by fusion processes, are made now joinable by the friction stir welding (FSW) process. The major advantage in FSW process is that the maximum temperature reached is less than 80% of the melting temperature (Tm), i.e. the joint is performed in the solid-state and excessive microstructural degradation of the weld zone is avoided. The correlation between the microstructure characteristics and strength properties during welding is one of the most important issues in FSW optimization. This report aims to collect large amount of information about friction-stir welded precipitation hardenable aluminium alloys applied worldwide, as well microstructural and mechanical properties more specifically, by considering second phase particles, dynamical recovery and recrystallization.