Research on the Mechanism of Oxygen-Induced Embrittlement Fracturing in Industrial Electrolytic Nickel

In this study, severe cracking occurred during an investigation of the direct hot rolling of industrial electrolytic nickel plates. To determine the cause of hot-rolling cracking, the microstructure phase composition was analyzed through the utilization of various techniques, including optical microscopy, scanning electron microscopy, electron backscattering diffraction, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and electron probe micro-analysis. The comparative microstructural analysis took place between specimens heat treated in atmospheric and vacuum environments. The characterization and analysis of the hot-rolled plates considered the crack microstructure and fracture morphology. It was shown that holes appeared along the large angular grain boundaries after annealing at 1100 °C for 8 h. Possible reason: In a high-temperature environment, the decomposition of residual additives in the electrolytic nickel releases oxidizing gases, which oxidizes the grain boundaries. The reaction with carbon diffused into the grain boundaries and produced carbon monoxide gas, which induced holes and severely reduced the grain boundary plasticity. The heat treatment time did not need to be very long for severe grain boundary degradation to occur. After severe cavitation, the electrolytic nickel was severely cracked at grain boundaries cracks due to a shear force, and brittle fractures occurred along grains with very low plasticity.

Effect of Turning Amount on Metallurgical Qualities and Mechanical Properties of GH4169 Superalloy

The determination of an appropriate amount of turning for superalloy ingot surfaces, in a scientific and reasonable manner, is vital to the improvement of the metallurgical quality and comprehensive performance of superalloy ingots. In the present study, scanning electron microscopy with energy-dispersive spectroscopy, a high-temperature testing machine, a Brinell hardness tester and the Image-Pro Plus software were used to analyze and compare the types and amounts of inclusions, the average area of the (Al,Mg)O inclusions, and the mechanical properties of points at different distances from the edge of the GH4169 superalloy vacuum arc remelting (VAR) ingot edge. The effects of the amount of turning to which the superalloy is subjected, the metallurgical qualities, and the mechanical properties were systematically studied. The results showed that the five inclusion types did not change as the sampling locations moved away from the ingot edge, but the amount of inclusions and the average area of the (Al,Mg)O inclusions first decreased and then stabilized. Similarly, the tensile strength, elongation, section shrinkage, hardness, and fatigue life first increased and then stabilized. Finally, this experiment tentatively determined that an appropriate amount of turning for a GH4169 superalloy ingot is 36–48 mm.

Mechanical and microstructural properties of fixation systems used in oral and maxillofacial surgery

OBJECTIVES

This paper aims to evaluate in vitro the mechanical and microstructural properties of internal fixation systems used in oral and maxillofacial surgeries.

MATERIALS AND METHODS

Four brands of internal fixation systems (screws and 4-hole straight plates) were selected and assigned to four groups: G1 Leibinger®, G2 Tóride®, G3 Engimplan®, and G4 Medartis®. The systems were submitted to Vickers hardness testing, metallographic and interstitial elements chemical composition analyses. Data were submitted to ANOVA and Tukey's test for statistical analysis.

RESULTS

Plates in groups 1, 2, and 3 showed similar microstructure and mechanical properties, different from those in G4 revealing larger grains. In all groups, the screws showed similar microstructure, with uniform arrangement and size of grains; the screws showed higher hardness values than those observed for the plates.

CONCLUSIONS

The results indicate that all materials tested are adequate for use in oral maxillofacial surgeries.