Papers by Keyword: Hardness

Abstract: In work the analysis of influence of structurization and nonmetallic inclusions on regularity of change of growth rate of a fatigue crack in different zones of a welded seam of steel X65 is carried out. Welded seams of the pipelines received by a combined method of welding of STT+API were investigated. Growth rate of a fatigue crack low in a root of the seam received when welding in the way STT. On border of the fatigue crack passing in the filling layers of a welded seam the inclusions which are settling down chains on borders of grains are found, being concentrators of tension.

Abstract: Potential difference between two phases in the Ti-6Al-4V alloy results in the galvanic cell reaction and corrosion. In order to improve the properties of Ti-6Al-4V, it was treated under different temperature with the atmosphere of 5vol. % oxygen and 95 vol. % nitrogen. The results showed that the titanium alloy surface is formed a layer of oxide and nitride compound layer. Sample treated at the temperature of 800°C had the most outstanding corrosion resistance and mechanical property.

Abstract: The work deals with the observation of microstructure and crack propagation from macro-indentation in a set of newly developed materials. Complex composites based on SiC matrix with 30, 40 and 50 wt. % of additives (Ti and NbC) were hot pressed at 1960 oC in air atmosphere under 30 MPa pressure for 1.5 hour. The microstructure and chemical composition were studied by SEM equipped with EDX analyzer. Hardness of the composites was evaluated by means of classic Vickers macro-indentation and fracture toughness was determined by the Anstis method. Indentation cracks were observed and their propagation was analyzed. The electrical conductivity as function of volume fraction of additives was determined.

Abstract: The Oliver–Pharr method has extensively been adopted for measuring hardness and Young’s modulus by indentation techniques. However, the method assumes that the contact periphery sinks in, which limits the applicability to the materials pile-up [1]. In this work, we characterize the pile-up (shape and height) in steel sheets with different mechanical properties and propose an improved methodology to calculate the real mechanical characteristics of steel sheets with significant pile-up. Pile-up correction of mechanical characteristics is based on ratio of pile-up height and contact depth. Pile-up height was measured by atomic force microscopy (AFM).

Abstract: The Shore A hardness, tensile stress at specified elongation (100, 200, and 300%), and compression stress at given strain (20 and 40%) of moulded natural rubber pads were modeled as function of ingredient proportions. Nine ingredients of the rubber pad were chosen as factors and varied at two levels of proportions. A 2^9-5 fractional factorial design of experiment was utilized during rubber compounding. Results show hardness of rubber pads is significantly increased when proportions of carbon black, tetramethylthiuram disulfide (TMTD), and stearic acid are increased in the formulations; hardness is decreased when process oil, paraffin wax, and antidegradant are increased. The same effect of carbon black, process oil, paraffin wax, and TMTD is observed on tensile properties of rubber pads. Compression properties are improved when carbon black, zinc oxide, and antidegradant are increased; properties are lowered when process oil and paraffin wax are increased. Analysis of variance shows the variation of response with ingredient proportion is significantly linear. The derived empirical models show good agreement with experimental data.

Abstract: Microstructure and sliding wear properties of the sub-microcrystalline pure iron produced by an HPT process were investigated in detail. It was found the grains of pure iron were significantly refined to the submicron size range by an HPT process, and the Vickers hardness of HPT-processed specimens increased with increasing number of turns and distance from the center due to the grain refinement. A linear relationship between the hardness and the inverse square root of grain size (the Hall-Petch relationship) was realized. The HPT process clearly increased the wear resistance, and a linear correlation between the specific wear rate and the inverse of the Vickers hardness was found, which agreed with the Archard wear equation. The wear in SUJ2 ball wear tests was much higher than that in WC-Co ball wear tests owing to the high adhesion between the specimen materials.

Abstract: In this work, Charpy notch pendulum impact test was performed on non-welded and TIG (Tungsten Inert Gas) welded Inconel 718 specimens at three different temperatures as 20°C, 500°C and 700°C. After the completion of tests, SEM (Scanning Electron Microscopy) inspection and EDX (Energy-Dispersive X-Ray Spectroscopy) analysis were performed for the microstructural examination of the specimens. Hardness measurements on the rupture zone of selected welded and non-welded specimens were also performed to make a better approach to interpretation of the impact behavior of material. Inspections indicated that hardness values in the heat affected zone of welded specimens dramatically decreased and they displayed higher ductility during fracture than non-welded samples due to partial softening of structure. The reason of further decrease in impact resistance of welded specimens was explained as the precipitation and coarsening of γ′′ and carbide phases in the interdendritic regions with increasing temperature.

Abstract: Deposition of NiCr-CrC(20NiCr) metal matrix composite (MMCs) coating have been applied on the substrate of boiler tubes material with High Velocity Oxygen Fuel (HVOF) thermal spray method and constant parameter. Variation of particle size and composition on MMCs was conducted to determined the optimum conditions for boiler applications. Microvickers hardness, metallography and thermal shock resistance testing were investigated. The best performance for boiler tubes application is MMC NiCr-CrC(20NiCr) with 270 mesh of NiCr particles size and 60:40 of composition as evidence by the highest of hardness value (410 Hv) and slightly of discoloration after thermal shock resistance with two variation cooling medium. While at MMC NiCr-CrC(20NiCr) with 70:30 variation composition, coating hardness value will decrease in line with the smaller of particle size of NiCr.

Abstract: Civil engineers like to use complex construction systems which resist mechanical strain well. Complex material and structural arrangement is possible to see in biological materials as wood but as bone or dentin too. This paper deals with a property trend of biological material, dentin, and can serve as an inspiration for designing resistant constructions. The analysis was carried out by a method of nanoindentation. The differences of property values depending on location of indents in dentin structure were surveyed. Especially, the differences of hardness and reduced modulus were important. The huge number of indents was made during the experiment. The indents were divided into categories according to the distance from the nearest material interface. The upward trend was found out for both observed properties. The category which was the closest to the material interface showed the average value of hardness ~ 965 MPa, whereas the furthest ~ 1222 MPa. It was growth more than 20%. Reduced modulus showed similar trend. These results are different from these which have been performed by other authors so far.

Abstract: The microstructure and mechanical properties of zirconia toughened alumina (ZTA) ceramic added with niobia (Nb₂O₅) through cold isostatic pressing (CIP) method was investigated. The amount of Nb₂O₅ is varied from 0 wt.% to 7 wt.%. The phase composition of the sintered bodies was analyzed with an x-ray diffractometer, while their microstructure was observed with a scanning electron microscope. It is found that up to 3 wt.% of Nb₂O₅ addition, the secondary phase of Nb₂Zr₆O₁₇ presence as square shape particles confirm by SEM and EDX. The addition of 3 wt.% showed the highest Vickers hardness value with 1600HV. It was observed that, further addition of Nb₂O₅ (> 3 wt.% ) deteriorates the Vickers hardness of ZTA. While the fracture toughness value increased at 3 wt.% until 5 wt.% of Nb₂O₅ addition (6.71 MPa · √m and 6.80 MPa · √m respectively). It was also found that the value for bulk density increased and porosity decreased with the increasing of Nb₂O₅ addition.