Renato Chaves Souza

The effect of WC-17Co thermal spray coating by hvof and hard chromium electroplating on the fatigue life and abrasive wear resistance of AISI 4340 high strength steel

One of the most interesting alternatives for replacement of hard chrome plating is tungsten carbide thermal spray coating applied by the high velocity oxy-fuel (HVOF) process which presents a safer, cleaner and less expensive alternative to chromium plating. The objective of this research is to compare the influence of the tungsten carbide-17cobalt (WC-17Co) coating applied by high velocity oxy fuel (HVOF) process with that of hard-chromium electroplating on the fatigue strength and abrasive wear of AISI 4340 steel.

Effect of a Shot Peening Pre Treatment on the Fatigue Behaviour of Hard Chromium on Electroless Nickel Interlayer Coated AISI 4340 Aeronautical Steel

Multiple layer systems of coatings are considered to have larger resistance to crack propagation in comparison to coatings with simple layer. With regard to fatigue, it is possible to improve the resistance of a component with the application of shot peening treatment, whose compressive residual stresses delay or eliminate the initiation and propagation of fatigue cracks. The aim of this study is to analyse the effects on rotating bending fatigue behaviour of hard chromium ¾ electroless nickel multilayer system coated AISI 4340 high strength steel submitted to shot peening pre treatment. Results indicated that the interaction between the shot peening process with the multilayer system was not satisfactory, resulting in intense delamination. Fracture surface analysis by SEM was performed toward to identify the fatigue crack origin, as well as the coating-substrate delamination process.

Mechanical Behaviour of ZrO2-Bioglass Dental Ceramics under Cyclic Fatigue Loading

The cyclic fatigue life of 3mol%Y2O3-stabilized ZrO2 (3Y-TZP) ceramics doped with bioactive glass has been investigated. Samples of 3Y-TZP containing 3 or 5wt% of bioglass were sintered at 1300oC for 120 minutes. Sintered samples were characterized by relative density, XRD and SEM analysis. Mechanical properties of hardness and fracture toughness were determined using Vickers indentation method and Modulus of Rupture was determined by four-point bending testing. Furthermore, the reliability of the samples was estimated using Weibull statistic analysis. The cyclic fatigue life was estimated using four-point bending testing under frequency of 25Hz and stress ratio, R, of 0.1. Highly dense tetragonal ZrO2 samples were obtained after sintering and presented hardness of 10.5 and 11GPa, KIC of 6 and 7MPam1/2, bending strength of 320 and 450MPa and Weibull’ modulus of 6 and 7 for samples containing 5 or 3% of bioglass respectively. The fatigue behavior indicates that the increasing of stress level leads to decreasing of the number of cycles and the number of run-out specimens. Fatigue behavior was similar for the two compositions tested. Samples containing 3% of bioglass are more resistant (near 10%) to fatigue presenting cyclic fatigue life near to 250MPa while samples with 5% presented fatigue limit near to 220MPa.

Fatigue of Zirconia - Bioglass Dental Ceramics

In this work the cyclic fatigue life of 3mol.%Y2O3-stabilized zirconia polycrystalline ceramics, doped with 5%wt 3CaO.P2O5,-SiO2-MgO, has been investigated. Samples with 5 and 10%wt were cold uniaxial pressed (80MPa) and sintered in air at 1200 and 1300oC for 120 minutes. Sintered samples were characterized by X-Ray diffraction and Scanning Electronic Microscopy. Hardness and fracture toughness were determined using Vicker’s indentation method, and Modulus of Rupture was determined by four-point bending testing. Furthermore, the cyclic fatigue tests were also realized by four-point bending tests, under frequency of 25 Hz and stress ratio, R, of 0.1, for the best condition. In this condition, highly dense samples were obtained and presented values of hardness, fracture toughness and bending strength of 11.3 ±0.1GPa, 6.1±0.4MPa.m1/2 and 320±55MPa, respectively. The increasing of stress level leads to decreasing of the number of cycles and the number of run-out specimens. The stress induced tetragonal-monoclinic (t-m)-ZrO2 transformation, observed by X-Ray diffraction, contributes to the increasing of the fatigue life. Samples 3Y-TZP presents clearly a range of loading conditions where cyclic fatigue can be detected.

Effect of La2O3-Rich Glass Addition on Sintering of Zirconia Based Ceramics

In this study, the influence of La-rich glass addition and sintering conditions on the densification and mechanical properties of 3 mol.%Y2O3-stabilized tetragonal zirconia polycrystals (3Y-TZP) ceramics were evaluated. High-purity tetragonal ZrO2 powder stabilized with 3 mol.% Y2O3 and La2O3-Rich glass were used as starting powders. Two compositions, ZrO2 containing 5 and 10 wt.% of a La2O3-rich glass were studied in this work. The starting powders were mixed/milled by planetary milling, dried at 90°C for 24 hours, sieved through a 60 mesh screen and uniaxially cold pressed under 80 MPa. The samples were sintered in air at 1200, 1300 and 1400°C for 60min, and at 1450°C for 120min, with heating and cooling rates of 10°C/min. Sintered samples were characterized by relative density, X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The mechanical properties, hardness and fracture toughness, were obtained by Vickers indentation method. Dense sintered samples were obtained for all conditions. Samples sintered at 1300°C for 60 min presented the optimal mechanical properties with hardness of 1170 kgf.mm-2 and fracture toughness of 8.3 MPam1/2.