This work aims to investigate the role of epoxy addition in high density polyethylene (HDPE) matrix. The block copolymer polyethylene-b-poly (ethylene glycol) (PEG-co-PE) was used as a compatibilizer. The samples were obtained by melt mixing using a torque rheometer. Instrumental nanoindentation was used to determine Young's modulus and nanohardness, thermal properties were analyzed by differential scanning calorimetry (DSC) and phase morphology was investigated through transmission and scanning electronic microscopy. The epoxy addition increased HDPE crystallinity by 13% and Young's modulus by 8%. The addition of PEG-co-PE decreased the size of dispersed phase by approximately 50% and improved phase adhesion and homogeneity compared to the blends without block copolymer. The experimental results were compared to numerical results obtained from the use of the homogenization by asymptotic expansion approach. The numerical results presented a fair agreement to the experimental values.

ABSTRACT In this paper, nanocomposites with multiwalled carbon nanotubes (MWCNT) or graphene nanosheets were prepared using a high density polyethylene (HDPE) matrix. Two different processes were employed: a solution method and a melt mixing method. The crystallinity index of the HDPE showed similar levels in nanocomposites after the addition of carbon nanotubes. It can be seen that the preparation process modified the degree of crystallinity of the HDPE matrix with graphene nanosheets. Nanocomposites prepared by the solution method showed a decrease in the crystallinity index. The addition of carbon nanotubes led to an increase of Young's Modulus with an increase in the MWCNT quantity, regardless of the preparation process used, with a 22.8 % increase for composites with 0.5 wt% of CNTs. The nanocomposites with graphene nanosheets exhibited a different behavior with each mixing method. Nanocomposites prepared by the solution method showed a higher Young's Modulus than those prepared by melt mixing. Results of transmission electronic microscopy and field emission scanning electronic microscopy indicated homogeneous dispersion for carbon nanotubes in melt mixing. Graphene nanocomposites showed some agglomerates, with smaller platelets in the nanocomposites prepared by solution mixing compared to that prepared by the melt mixing.

In this work, nanocomposites with simultaneous dispersion of carbon nanotubes and clays in a high density polyethylene (HDPE) matrix were prepared. Two different processes of preparation were employed: solution or melt intercalation. Two different montmorillonite clays were used separately: a natural (MMT-Na) or an organoclay (MMT-30B) and it was used multiwalled carbon nanotubes (MWCNT). Thermal properties were evaluated by DSC and TGA, mechanical properties were evaluated by nanoindentetion and morphology was investigated by transmission electronic microscopy (TEM). Alterations of 20% in crystallinity were detected, increases in Young´s modulus up to 12% were observed and up to 20% of increase was observed in Oliver-Pharr hardness. It is possible to explain part of those results based on the state of dispersion observed in our TEM results.

The corrosion properties of a 22.5 wt. (%) Cr duplex stainless steel were investigated after long-term aging of 3000, 5000 and 7000 hours at 300 and 400 ºC. The corrosion resistance was measured based on mass loss in a FeCl3 10 wt. (%) solution and electrochemical measurements in a 0.1 M H2SO4 solution. The results indicate that the corrosion resistance decreased steadily up to 5000 hours of aging. However, the samples subjected to 7000 hours of aging showed better corrosion resistance than those aged for 3000 and 5000 hours. This effect is attributed to the phase transformation that occurs during aging, a finding which was confirmed by hardness, transmission electron microscopy and X-ray photoelectron spectroscopy measurements.

Mechanical and tribological properties os AISI 304 and AISI 316 stainless steels submited to glow discharge ion nitriding are reported.The atmosphere was 20:80 - N2:H2 with substrate temperatures ranging from 300 to 500 °C. Treatment at 300 °C produced expanded austenite (γN) in both steels. Increasing the temperature, the phases γ´-Fe4N and - Fe2+xN were present and the latter is the major phase for AISI 304. At 500 °C, the CrN phase was also identified in both steels. Hardnesses of about 13-14 GPa at near surface regions were obtained in both steels. Moreover, AISI 316 nitrided at 500 °C has the deepest hard layer. Tribological tests showed that wear can be reduced by up to a factor of six after the nitriding processes, even for a working temperature of 300 °C. The profiles during and after nanoscratch tests did not reveal significant differences after nitriding processes in both steels.