In the past two decades, titanium foams have attracted greater interest from the biomedical industry due to their excellent chemical and mechanical biocompatibility when used as biomimetic implants. The porous structure plays an important role in bone adhesion to an implant, allowing its growth into the component. Moreover, the voids reduce the elastic modulus, promoting greater compatibility with the bone, avoiding the stress shielding effect. In this regard, metal injection molding is an attractive process for titanium foams manufacturing due to the high microstructural control and the possibility of producing, on a large scale, parts with complex near-net-shaped structures. In this review, recent discoveries and advantages regarding the processing of titanium powders and alloys via metal injection molding combined with the space holder method are presented. This approach can be used to obtain foams with high biocompatibility with the human body at a microstructural, chemical, and mechanical level.

Refined grain size structure is one of the most sought-after features during parameterization of welding processing. Refined grains in the region of the molten zone provide high tenacity in addition to high hardness, due to the dislocation blocking by grain boundaries. However, obtaining refined grain structure is not trivial, since a molten pool is formed during bonding of materials via welding, which often results in grain growth. In this sense, this study aimed to refine the granular structure of an SAE 1045 steel by modulating laser power. The success through the modulation method in some aspects of welding is well known from the literature, such as the reduction of pores and cracks as well as deep penetration with narrow heat affected zones. These enhancements are due to cooling rate control produced by the nonuniform way of interaction between the laser and the specimen. In the present study, 1045 steel specimens were first welded utilizing the conventional continuous mode and then the results were compared with a modulated rectangular-shaped power mode while maintaining the average power constant. Microhardness measurements were used in order to investigate the mechanical effect of grain size changes. It was found that an increase in hardness of 50 HV was achieved by modulating the laser power in time. This increase is credited to the reduction in grain size of the studied steel. It can be assumed that the time modulation of the laser power provides a better control of the cooling rate and consequently the mass flux in the molten pool, what may explain the hardening effect by grain refinement.

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To modify the surface structure of AISI 1005 steel and its properties without any dimensional loss, different plasma surface treatments were performed at low temperatures (500 °C) in this study. The samples were subjected to single plasma treatments including: nitriding (N5% and N3%), carburizing (CE) and ferritic nitrocarburizing (NC) and to duplex treatments of nitriding followed by carburizing (N5%+CE and N3%+CE) and ferritic nitrocarburizing followed by carburizing (NC+CE). The gas mixture used for these treatments was varied as follows: nitriding (5%N 2 +95%H 2 and 3%N 2 +97%H 2 ), carburizing (5%CH 4 +95%H 2 ) and ferritic nitrocarburizing (5%N 2 +1.5%CH 4 +93.5%H 2 ). A microstructural characterization of the samples was carried out using optical and scanning electron microscopy in addition to XRD analysis. Microhardness testing was also performed. The XRD analysis showed a stabilization of the outermost cementite layer for all of the carburizing treatments. The results show that a greater hardness increase was achieved for the nitriding treatment as well as a more regular compound layer. However, a greater depth of hardening was obtained in samples with NC+CE and N5%+CE, which extended to the hardened depth to 800 μm.

ResumoO desenvolvimento dos aços inoxidáveis significou um grande avanço na fabricação de materiais resistentes à corrosão. Dentre os aços inoxidáveis desenvolvidos, estão os aços inoxidáveis duplex (AID). Os AID são aços de baixo teor de carbono, ligados principalmente ao cromo, níquel e molibdênio que possuem composição balanceada, de modo a se obter uma microestrutura mista, com frações volumétricas aproximadamente iguais de ferrita e austenita. Este artigo apresenta uma visão geral sobre os aços inoxidáveis duplex, começando com um resgate do contexto histórico, dos processos de fabricação, da classificação, passando pelas propriedades mecânicas e metalúrgicas e finalizando com as principais aplicações desse material. Palavras

ResumoEste trabalho apresenta uma nova abordagem sobre o emprego sequencial dos tratamentos termoquímicos de superfície utilizando a tecnologia de plasma. No trabalho são avaliados tratamentos de superfície, individuais e sequenciais, de nitretação/cementação. Os tratamentos foram realizados no campo ferrítico com o objetivo de manter as tolerâncias dimensionais. Amostras de aços AISI 1005 foram tratadas em descarga luminescente anormal sendo realizados ciclos únicos de cementação e nitretação e também ciclos conjuntos de nitretação + cementação. Todos os tratamentos foram realizados a 500°C com um tempo de patamar de 3 horas para cada tratamento. A composição da mistura gasosa variou de acordo com o tratamento: nitretação -5%N 2 + 95%H 2 ou 3%N 2 + 97%H 2 ; cementação -5%CH 4 + 95%H 2 . A caracterização microestrutural das amostras foi realizada por microscopia óptica e MEV além de difração de raios-X. Análises de microdureza também foram realizadas. As analises de raios-X mostraram que ocorre a estabilização de uma camada de cementita nos tratamentos de cementação. Nas amostras nitretadas em atmosfera contendo 5% de N 2 foi observada a presença de camada de compostos. Já em atmosferas contendo 3% de N 2 não houve a formação da camada de compostos. A maior profundidade de endurecimento foi obtida para a amostra nitretada + cementada. Palavras-chave: Tratamentos termoquímicos sequenciais; Plasma; Caracterização microestrutural. SURFACE THERMOCHEMICAL TREATMENTS BY PLASMA IN AISI 1005 STEEL AbstractThis paper presents a new approach on the sequential use of surface thermochemical treatments by plasma technology. Single and sequential treatments of nitriding/carburizing are evaluated in this work. The treatments were performed in the ferritic field with the objective of maintaining the dimensional tolerances. AISI 1005 steel samples were treated in an abnormal glow discharge being carried out only carburizing, nitriding, ferritic nitrocarburizing cycles and also sequential cycles of nitriding + carburizing. All treatments were conducted at 500 ° C with a hold time of 3 hours for each treatment. The composition of the gas mixture varied with the treatment: nitriding -5%N 2 + 95%H 2 or 3%N 2 + 97%H 2 ; carburizing -5%CH 4 + 95%H 2 . The microstructural characterization of the samples was carried out by optical and scanning electron microscopy in addition to X-ray diffraction. Microhardness tests were also performed. The X-ray analysis showed the stabilization of a cementite layer in carburizing treatment. In the nitrided samples in atmosphere containing 5% N 2 , it was observed the presence of a compound layer. Already in atmosphere containing 3% N 2 was no formation of a compound layer. The greater depth of hardening was obtained in samples nitrided + carburized.

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