Microstructure and Oxidation Behaviour of NGB and WGB Joints With Boron/Silicon Free Nickel Base Braze Alloys

In this study, the microstructure and solidus and liquidus of several Ni-Co-Hf-Zr-Ti-Al braze alloys were first examined with the objective to develop a B and Si free low melting braze alloy for narrow gap (NGB) and wide gap brazing (WGB) and turbine component repair applications. Among various alloys examined, DSC was used to measure the solidus and liquidus during heating and cooling cycles. Following the measurements of liquidus and solidus, the microstructure was evaluated using SEM. Equations for calculating solidus and liquidus based on alloy’s compositions were established and the functions of each elements on these two characteristic temperatures were discussed. One selected alloy with a liquidus of 1201 °C was further employed for NGB and WGB experiments. The results showed that it was able join CMSX-4 at 1240°C without interfacial voids; and with the use of externally applied pressure and extended homogenization treatment the interfacial intermetallic compounds were substantially removed. Furthermore, the same braze alloy was used to fill a large artificial cavity in a WGB scheme at a reduced temperature of 1200°C. The braze alloy was able to fully bond the filler powder alloy in addition to join the two alloys to a IN 738 substrate. Finally, oxidation test was conducted at 1050°C (isothermal in static air) for 100 hours after NGB of CMSX-4 and WGB of IN 738. The results showed that the oxide formed on the standalone braze alloy is very dense and there is no sign of spallation. It contained primarily NiO (+CoO) with no other elements measured. For the NGB joints, large amount of scale spallation was observed on base alloy CMSX-4 while the NGB joint remained spallation free. The oxide formed on the NGB was NiO with partitions of Co, Al, Ti, Cr, and W. The WGB joint region in IN 738 showed oxide scale spallation on the IN 738 substrate side, leaving behind steps and depression on the sample surface. In the WGB joint itself, there were three notable phases after oxidation test, however, no scale spallation could be found. For the majority part of the surface, a Ni-rich oxide covered the surface. There were areas of smaller oxide particles with higher Cr content. Overall, the new boron/silicon free braze alloy was found to be able to join several superalloys in both WGB and NGB schemes without occurrence of defects and the oxidation resistance was superior to both substrate alloys examined in this study.

The Study of Geomechanical Condition of Unstable Rocks in the Vicinity of Mine Working Junctions

The relevance of research of material strain nature based on physical models equivalent to rocks is substantiated. To identify the dependencies and mechanism of unstable rock strain in the vicinity of mine working junctions, an experimental technique has been developed and presented. The method of physical modeling using equivalent materials was applied in the research. Strength characteristics of the rock equivalent material were calculated using the formulas proposed by G.N. Kuznetsov. The equivalent material was prepared based on two components, sand and paraffin. The mix formulation was selected, and ultimate compressive strength of the equivalent material was determined. The experiment was performed for three options of the physical models: an intact rock mass, a rock mass with a single mine working, and a rock mass with mine working junctions. Testing of the models made of the equivalent material was performed through uniaxial vertical loading using a hydraulic press. Based on the model testing findings, the dynamics of fracture propagation and crushing of the enclosing equivalent material in the vicinity of an artificial cavity, simulating a mine working, has been demonstrated. Besides, the graphs of relative strain versus vertical loading for each stage of the stepwise loading of these three model options were produced. The findings of the strain-stress distribution modeling for the equivalent material around the cavities simulating mine working junctions were analyzed. The strain testing findings for the materials simulating rock behavior are expected to be used as the initial data for analysis of physical and numerical simulation, as well as for developing engineering documentation with regard to the selection of parameters for supporting mine working junctions.

ARGUMENT BASIS TO PROVE CHOICE OF FILLING MATERIAL FOR CERVICAL CARIES TREATMENT OF PATIENTS WITH INFLAMMATORY PERIODONTAL DISEASE DURING THE CURETTAGE OF GUMS WITH EXPERIMENTAL MODEL EXAMPLE

Background. The problem of choice of filling material in cervical caries treatment of patients with inflammatory periodontal diseases is considered in the article. It was evaluated the adaptation of filling materials to tooth tissues, as a result of mechanical some aggressive methods applied for treatment of periodontal tissues with curettes using ultrasonic apparatus. The following filling materials were suggested: composite light-curing filling material, hybrid composite light-cured material, and hybrid glass ionomer material with triple curing. Objectives. The aim of the work is to give arguments for the choice of filling material for cervical caries treatment of patients with inflammatory diseases of the periodontium during the treatment with the use of gingival curettage. Materials and methods. Carious cavities were artificially prepared on the teeth removed for surgical indications in the cervical areas and, according to the manufacturer's instructions, filled with: light-curing composite filling material, hybrid light-curing composite, hybrid glass-ionomer triple-curing cement and immersed for maturation at 37 °C into isotonic solution for 5 days. After that, there was removal of dental deposits and gum curettage carried out according to the Protocol developed by Moscow state medical and dental University under the name of A. I. Evdokimov, the Ministry of Healthcare, Russian Federation. The fillings were isolated with1 mm indentation from the edge of the insulating coating. All available cavities and apical holes of the roots are filled with wax. Then the teeth were placed in the eosin-B solution for 2 hours at a temperature of 37 °C. On the longitudinal saws in the center of the filling, a visual assessment of the edge permeability of the filling material was carried out using a Khera S .C., Chan K.C. five-point system. Results. The best results were obtained by light-curing composite filling material. So, it did not reveal the edge permeability of the filling material in 26 % of case and did not reveal any case of staining in the bottom of cavity. Also, in the composite of light curing, no staining of the bottom of artificial cavity was revealed. However, only 9 % of the samples had no permeability. In hybrid glass ionomer triple-cured cement, the greatest penetration of colorant beyond the edges of the artificial cavity was observed and amounted to 87 % of cases. Staining at the bottom of the artificial cavity was revealed in 13 % of cases. Summary. The carried out studies on experimental models have shown that after the gingival curettage the lowest indices of edge permeability and better adaptive properties has composedly light-curing material. It proved the best resistance to traumatic and aggressive factors. It is optimal to use a light-cured composite filling material to cure patients with inflammatory periodontal diseases in the cervical areas, with mandatory compliance in the stages of preparation, filling and polishing.

Wild chimpanzees select tool material based on efficiency and knowledge

Some animals have basic culture, but to date there is not much evidence that cultural traits evolve as part of a cumulative process as seen in humans. This may be due to limits in animal physical cognition, such as an inability to compare the efficiency of a novel behavioural innovation with an already existing tradition. We investigated this possibility with a study on a natural tool innovation in wild chimpanzees: moss-sponging, which recently emerged in some individuals to extract mineral-rich liquids at a natural clay-pit. The behaviour probably arose as a variant of leaf-sponging, a tool technique seen in all studied chimpanzee communities. We found that moss-sponges not only absorbed more liquid but were manufactured and used more rapidly than leaf-sponges, suggesting a functional improvement. To investigate whether chimpanzees understood the advantage of moss- over leaf-sponges, we experimentally offered small amounts of rainwater in an artificial cavity of a portable log, together with both sponge materials, moss and leaves. We found that established moss-spongers (having used both leaves and moss to make sponges) preferred moss to prepare a sponge to access the rainwater, whereas leaf-spongers (never observed using moss) preferred leaves. Survey data finally demonstrated that moss was common in forest areas near clay-pits but nearly absent in other forest areas, suggesting that natural moss-sponging was at least partly constrained by ecology. Together, these results suggest that chimpanzees perceive functional improvements in tool quality, a crucial prerequisite for cumulative culture.