The Microstructure Evolution of Fe-28Al-15Si-0.2Zr Alloy during Different Heat-Treatment

The structures of Fe-28Al-15Si-0.2Zr iron aluminide in the as cast state and in three states after heat-treatments (at 800 °C for 100 hours, at 1000 °C for 24 hours and at 1200 °C for 2 hours) were investigated for verification of secondary phases stability. The type and distribution of precipitates were described by means of light optical microscopy and scanning electron microscopy equipped with an energy dispersive analysis. The presence of complex carbides based on Fe-Si-Zr was shown. The bulk hardness and image analysis of samples was measured for verification of dissolution of secondary phase particles to the matrix. Short-term annealing did not influence distribution and dissolution of secondary particles significantly, while long-term annealing (at 800 °C for 100 hours) leads to the sporadic formation of fine eutectic areas.

Microstructure, Microhardness, and Wear Properties of Cobalt Alloy Electrodes Coated with TiO2 Nanoparticles

In this paper, the influence of TiO2 nanoparticle coating on cobalt-based electrodes was studied. Different coating treatment times were applied, and the results were compared to the hard-faced layer obtained with unmodified electrodes. The hard facing was done in three layers, the first being a Ni-based interlayer, followed by two layers of corrosion and wear-resistant Co-based Stellite 6 alloy. Pin-on-disc wear testing was applied, along with the metallographic study and hardness measurements of the hard-faced layers. Furthermore, energy-dispersive X-ray spectroscopy (EDS) analysis was conducted. It was found that the microstructural properties, as well as microhardness profiles, are modified in hard-faced layers obtained with modified electrodes. Interdendritic distances are altered, as are the dendrite growth directions. Titanium oxides are formed, which, along with the present complex carbides, increase the wear resistance of the hard-faced layers compared to layers obtained with untreated electrodes.

Crystal Chemistry of Ternary Rare Earth Transition Metal Carbides: Studies of the Tb-Fe-C System at 800°C

The isothermal section of the phase diagram of Tb–Fe–C system at 800 °C was studied in the full concentration range using powder X-ray phase and structure analyses, and energy-dispersive X-ray spectroscopy. Six ternary compounds Tb1.88Fe14C, Tb13Fe10C13, TbFeC2, Tb15Fe8C25, Tb5.64Fe2C9, Tb2FeC4 and a limited solid solubility of carbon in the crystal structure of the binary parent compound Tb2Fe17Cх (0≤ х ≤0.8) have been found to exist at 800 °C. The crystal structures of two new ternary carbides have been determined by means of powder X-ray diffraction: Tb15Fe8C25 with structure type Er15Fe8C25, space group P321, a = 11.9706(3) Å, c = 5.1733(2) Å, RB(I) = 0.07, RP = 0.06, RPw = 0.08, and Tb13Fe10C13 with structure type Gd13Fe10C13, space group P3121, a = 9.1800(9) Å, c = 23.703(5) Å, RB(I) = 0.04, RP = 0.16. Both compounds are representatives of the carbometalate class of complex carbides. Tb15Fe8C25 displays an itinerant ferro-or ferrimagnetic ordering of the Fe 3d-moments below TM ≈ 50 K while Tb 4f-moments remain essentially paramagnetic at least down to about 10 K.

Creep Damage Mechanisms in Cast Cobalt Superalloys for Applications in Glass Industry

Two cast NbC and TaC- strengthened cobalt-base superalloys have been developed for a precision casting of spinner discs for glass wool industry. In the present study, the relationships between the type and morphology of carbides and the degradation processes in both types of cast cobalt-based superalloys subjected to high temperature creep have been examined. It was found that the nature of carbides within the alloy microstructure plays a critical role in determining the creep damage processes and microstructure stability of the alloy system under high temperature creep. The morphology of the carbides is a strong function of their chemical composition. The interface decohesion between the complex carbides and the matrix and cracking of the brittle carbides homogeneously distributed in the crept NbC - strengthened alloy lead to brittle intergranular and/or interdendritic fracture. By contrast, Ta - strengthened alloy exhibited very small extent of isolated creep damage and the final fracture is ductile transgranular mode.

Aspects Regarding Repetitive Maintenance Concept in Push Blades for Loading Equipment

Preventive repeated maintenance concept provides elaborating, developing and reconditioning, repeatedly, in economic efficient conditions, of the pushing blades that equip bulk loading machines, namely leveling them. Applying the solution implies developing and elaborating active areas in direct contact with processed materials by loading through welding. To this end the base material of the blades is chosen to comply with the addition material afferent to the selected process, for predetermined circle tries, approx. 5 in the present moment.Research conducted to validate the loading through welding technology had primary objectives to obtain material couples base/addition that have a high resistance to intense bending demands, under load, combined with a good abrasion usage resistance or high pressure. The chemical composition of the basic materials in the pushing blades, is afferent to high resistance steels, with a maximum of1.6%Mn, max. 1.5%Cr, max.2%Ni, max. 0.7%Mo and max. 0.005%B. The chemical composition of the deposited material, through welding, falls into steel prescription, type Fe-25%Cr-5%W-Nb-Ti-B, with metallographic structures that have a high content of complex carbides and hardness of minimum 60 HRC. Sclerometric tried and metallographic research of specific area of the deposited metal/base metal ensemble did not highlight any imperfections such as cracks or white sports in the thermal influenced areas.Research regarding exploitation behaviour, of basaltic aggregates in loading conditions or cereals, have shown a good resistance at wear.

Precipitation of Nano-Sized Carbides in a Ti-Mo Bearing Steel at a Low Transformation Temperature

While the role of Ti and Mo elements on precipitation strengthening in ferrite grains formed during austenite/ferrite transformation is very clear, some uncertainty still presents concerning influence of microalloying elements on bainite transformation. Therefore, the present study focuses on the precipitation behavior occurred in a Ti-Mo bearing steel during bainitic phase transformation under different heat treatment conditions, and the correlation of the precipitation behavior with hardness distribution. Through the present work, it is expected to achieve a better understanding of low-temperature precipitation behavior to assist metallurgists to find out the reason for maintaining a high hardness by longtime isothermal holding, which can provide insight to design a better quality steel product. Vickers hardness was measured from the 1C-2Ti-2Mo, 1C-2Ti-2Mo and 0.5C-1Ti-2Mo steels treated by isothermal holding at 550 oC for 5 to 60 min. The average Vickers hardness was in the range of 245 - 276, 290 - 335 and 220 - 245, respectively. Therefore, higher hardness can be obtained if the steel containing higher carbon and microalloying elements can form precipitations in the ferrite matrix. On the other hand, increasing Vickers hardness with isothermal holding times indicates a good thermal stability character of complex carbides. The excellent thermal stability can be attributed to the addition of Mo element, which can inhibit the growth of carbides during longtime isothermal holding. Furthermore, the addition of Mo in the steel can avoid annihilation of dislocations during longtime aging. By taking advantages of these two effects, high strength can be achieved for high-strength low-alloy steels containing Mo element. Transmission electron microscopy image showed nano-sized carbides nucleated at dislocations, instead of interfacial precipitations within ferrite grain matrix, because the interface precipitation morphology only occurred accompanying the austenite decomposition reaction. However, the bainitic phase transformation was of a displacive transformation character, thus the complex carbides could not form during the bainitic phase transformation due to a very fast transformation velocity.