Abstract This work presents a study on effect of cutting parameters in force, texture and chips morphology obtained during the turning of a self-lubricating sintered composite. The tests were performed varying the cutting speed (vc = 100 and 200 m/min), feed (f = 0.1 and 0.2 mm), depth of cut (ap = 0.5 and 1 mm), as well as the materials manufacturing route in single pressing (SP) and double pressing (DP). The variation in the cutting parameters influenced the components of the machining force. The cutting, feed and passive force were approximately 10%, 10% e 25% higher, respectively, for DP materials. The turning process generated surfaces with values of maximum height (Sz) between 28.3 to 10.8 μm, Kurtosis (Sku) > 3 and Skewness (Ssk) < 0.3. The chip type obtained was segmented and the chip thickness ratio was influenced by the variation of the cutting parameters and the materials manufacturing route.

The objective of this work is to investigate the influence of the crystallographic texture on the corrosion resistance of 16% Cr ferritic stainless steel. Samples of ASTM S43000 ferritic stainless steel, both niobium-stabilised and non-stabilised, were used. The samples were subjected to crystallographic characterisation (EBSD) and analysed using an inverse pole figure (IPF) and a crystalline orientation distribution function (CODF). The samples also underwent anodic potentiodynamic polarisation tests (deaeration by high-purity argon gas) in 3.56% NaCl and 1N H2SO4 solutions, and the surface was examined by SEM after the tests. The results showed a clear influence of the crystallographic texture on the corrosion resistance. The niobium decreases the amount of the preferred orientation and thus the influence of the texture on the corrosion resistance, although the corrosion resistance of the stainless steel is increased as niobium carbides are formed.

When multifunctional surface engineering processes that combine purpose-oriented phases are applied to soft substrates, a combination of high wear resistance, high load support and low coefficients of friction can be achieved. In this study, the effects of different nitrided layers on the tribological behaviour of a diamond-like carbon (DLC) film deposited on a SAE 1040 steel were investigated. The nitriding was carried out under different temperatures and gas mixtures to create three distinct nitrided layers: two compound layers with predominant ε and γ' phases and a diffusion layer. All of the surfaces were then coated with DLC deposited via plasma-enhanced chemical vapour deposition (PECVD). The tribological tests indicated that the best performance was achieved for a specific combination of hardness, surface roughness and nitride type. The best load-bearing capacity between the DLC coating and the soft substrate was achieved when the nitrided layer was primarily a diffusion layer.

O objetivo deste estudo foi caracterizar a microestrutura de uma superfície de titânio comercialmente puro (cpTi) condicionada com HCl/H2SO4 (acid etched) (AE-cpTi) e investigar sua citocompatibilidade in vitro, comparada à do cpTi usinado (turned) (T-cpTi). O T-cpTi apresentou uma superfície com sulcos e o AE-cpTi exibiu uma superfície caracterizada pela presença de micro-vales. Os parâmetros de superfície indicaram que a superfície AE-cpTi é mais isotrópica e apresenta uma área maior quando comparada à superfície T-cpTi. A espessura da camada de óxido foi similar para as duas superfícies; no entanto, a AE-cpTi apresentou maiores quantidades de Ti e O e menor, de C. A proliferação de células osteoblásticas, a atividade de fosfatase alcalina e a formação de matriz mineralizada foram maiores na superfície T-cpTi que na AE-cpTi. Esses resultados mostram que o condicionamento ácido produziu uma superfície com características topográficas e químicas diferentes quando comparadas às da superfície usinada. Além disso, observou-se que essas modificações de superfície afetaram de forma negativa a citocompatibilidade in vitro do cpTi como demonstrado pela inibição da proliferação celular e da expressão do fenótipo osteoblástico.

The aims of this study were to characterize the microstructure of a commercially pure titanium (cpTi) surface etched with HCl/H2SO4 (AE-cpTi) and to investigate its in vitro cytocompatibility compared to turned cpTi (T-cpTi). T-cpTi showed a grooved surface and AE-cpTi revealed a surface characterized by the presence of micropits. Surface parameters indicated that the AE-cpTi surface is more isotropic and present a greater area compared to T-cpTi. The oxide film thickness was similar between both surfaces; however, AE-cpTi presented more Ti and O and less C. Osteoblastic cell proliferation, alkaline phosphatase activity, and bone-like nodule formation were greater on T-cpTi than on AE-cpTi. These results show that acid etching treatment produced a surface with different topographical and chemical features compared to the turned one, and such surface modification affected negatively the in vitro cytocompatibility of cpTi as demonstrated by decreasing culture growth and expression of osteoblastic phenotype.

Noncarious cervical lesions (NCCLs) are considered to be of multifactorial origin, normally associated with inadequate brushing. This study assessed the influence in vitro of simulated brushing on NCCL formation. Fifteen human premolars were submitted to brushing in the cementoenamel junction region, using hard-, medium- and soft-bristled brushes associated with a toothpaste of medium abrasiveness under a 200 g load, at a speed of 356 rpm for 100 minutes. The surface topography of the region was analyzed before and after brushing, by means of a laser interferometer, using "cut-off" values of 0.25 and considering roughness values in mm. The initial roughness (mm) results for dentin (D / bristle consistency: 1 - soft, 2 - medium and 3 - hard) were as follows: (D1) 1.25 ± 0.45; (D2) 1.12 ± 0.44; (D3) 1.05 ± 0.41. For enamel (E / bristle consistency: 1 - soft, 2 - medium and 3 - hard), the initial results were: (E1) 1.18 ± 0.35; (E2) 1.32 ± 0.25; (E3) 1.50 ± 0.38. After brushing, the following were the values for dentin: (D1) 2.32 ± 1.99; (D2) 3.30 ± 0.96; (D3) Over 500. For enamel, the values after brushing were: (E1) 1.37 ± 0.31; (E2) 2.15 ± 0.90; (E3) 1.22 ± 0.47. Based on the results of the ANOVA and Tukey statistical analyses (a = .05) it was concluded that soft, medium and hard brushes are not capable of abrading enamel, whereas dentin showed changes in surface roughness by the action of medium- and hard-bristled brushes.

Durability of surfaces has been reported as the main factor affecting tribological behavior of steam oxidised sintered iron. The presence of surface pores and their negative influence on load bearing capacity, suggest that surface topography might play an important role on the durability of the oxide layer. In this paper, the influence of compaction pressure and powder grade on surface topography, and as a consequence, its effect on the tribological behavior of steam oxidised sintered iron has been analysed. Specimens prepared from atomised iron powders with different sizes were compacted using 4 different pressures, sintered, and then subjected to steam treatment. Tribological characterisation was carried out in a reciprocating sliding wear test. Although the processing parameters affected the surface topography to a considerable extent, the main influence may be attributed to powder grade. A strong influence of surface topography on the durability distance, evaluated in terms of the evolution of contact resistance with total sliding distance, has been highlighted. Surfaces which were smoother and had high load-carrying capacity were always associated with a higher durability distance.