The Influence of the Soaking Temperature Rotary Forging and Solution Heat Treatment on the Structural and Mechanical Behavior in Ni-Rich NiTi Alloy

The structural and thermophysical characteristics of an Ni-rich NiTi alloy rod produced on a laboratory scale was studied. The soak temperature of the solution heat-treatment steps above 850 °C taking advantage of the precipitate dissolution to provide a matrix homogenization, but it takes many hours (24 to 48) when used without thermomechanical steps. Therefore, the suitable reheating to apply between the forging process steps is very important, because the product’s structural characteristics are dependent on the thermomechanical processing history, and the time required to expose the material to high temperatures during the processing is reduced. The structural characteristics were investigated after solution heat treatment at 900 °C and 950 °C for 120 min, and these heat treatments were compared with as-forged sample structural characteristics (one hot deformation step after 800 °C for a 30 min reheat stage). The phase-transformation temperatures were analyzed through differential scanning calorimetry (DSC), and the structural characterization was performed through synchrotron radiation-based X-ray diffraction (SR-XRD) at room temperature. It was observed that the solution heat treatment at 950 °C/120 min presents a lower martensitic reversion finish temperature (Af); the matrix was fully austenitic; and it had a hardness of about 226 HV. Thus, this condition is the most suitable for the reheating stages between the hot forging-process steps to be applied to this alloy to produce materials that can display a superelasticity effect, for applications such as crack sensors or orthodontic archwires.

Development of the technology of «Mozzarella» goat cheese with specified functional properties

The article shows the prospects for the production of Mozzarella cheese of goat milk and dry sourdough. Cheese contains vital nutritional components, they are biologically complete and play an important role in the diet. Searching for new resources is an urgent problem. The solution may be to expand the range of cheeses not only of cow milk, but also of other farm animals, for example, goats. Their milk is absorbed faster and is used in medical and preventive nutrition. On the consumer market goat milk products are mainly represented by farms, and their range is small. The authors carried out the research on the selection of starter cultures containing probiotic cultures from bifidobacteria, acidophilus bacillus and thermophilic streptococcus, to optimize the technological process for the production of Mozzarella cheese based on goat milk. These cultures represent a beneficial microflora that inhabits the human body, helping to absorb nutrients and digest food. An important quality of probiotics that ensures their physiological effect is their high growth rate and compatibility with other microorganisms present in the gastrointestinal tract. It has been found that all the studied samples of goat milk in terms of composition have indicators that meet the requirements of GOST for goat milk. Comparative analysis of cow and goat milk has shown predominant indicators of the quality of goat milk in comparison with cow milk. The processes of coagulation and fermentation of goat milk under the influence of various starter cultures have been studied. The use of ABT-5-Probio-TecTM probiotic starter culture, which accelerates the technological process and imparts functional properties to the product, has been substantiated. The possibility of using goat milk in the production of cheeses with cheddaring and thermomechanical processing has been proven. Microscopic examination of a sample of Mozzarella cheese on ABT-5 sourdough has shown that bifidobacteria survive after heat treatment at high temperatures.

Methods for obtaining a dispersed structure and increasing the strength of silicon-manganese steels

For high-strength structural steels, the problem of grinding grain and increasing strength is solved by the use of highly efficient technologies, the development of new steel compositions and the development of rational thermomechanical processing. Goal. The aim of the work is to transform the structure, study the methods of grain grinding and increase the strength properties of structural steels 09Г2, 09Г2С as a result of modification by nanodisperse compositions, heat treatment and intense plastic deformation. Methodology. The research material was structural low-carbon steels 09G2, 09G2S. The process of modifying the steel parameters of the geometric shape of the melts was carried out by smelting steels 09G2 and 09G2C in an induction furnace. The modified workpieces were subjected to intensive plastic deformation and heat-treating treatment according to the mode: heating temperature 1050 °C, exposure 5 min; cooled medium: water and 20 % solution of NaCl in water. Then – a rest at temperatures of 500 °C; 600 °C, exposure time – 30 minutes. Metallographic studies of the structure of steels before and after modification and mechanical testing of standard samples were performed. Results. The study of the structure grains of steels 09Г2 and 09Г2С in the initial state showed the presence of large grains up to 30 μm, reduced microhardness and yield strength. Originality. The substantiation of the choice of type and fraction of nanodisperse modifier was carried out. The use of plasma-chemical synthesis to obtain nanopowders based on titanium was substantiated. Nanopowders of titanium carbonitride Ti (CN) fraction 50 ... 100 nm were obtained by the method of plasma chemical synthesis. Practical value. The following methods were proposed for grinding grain and increasing the strength properties of steels: nanomodification, intensive plastic deformation in combination with heat-strengthening treatment.

Development of the technology of production of cheese ‘Suluguni’ for farms

The aim of the research is the development of a technology for the production of ‘Suluguni’ cheese for farms from milk of cows. Investigations of the chemical composition and physicochemical properties of cows’ milk were carried out using by ultrasonic method. It was found that the mass fraction of protein in milk is 3.19±0.02%, fat is from 4.32±0.06% to 5.07±0.08%. For the production of cheese, milk was standardized. The protein content in normalized milk is 3.37±0.02%, fat - 2.84±0.03%. The ratio of the mass fraction of protein and fat in normalized milk was 1.00:1.19. It was found that the milk of cows meets the requirements for raw materials for the production of cheese. We have developed a technology for the production of brine cheese ‘Suluguni’, which consists of the following operations: receiving milk, preparing milk for making cheese, fermenting, curdling and processing the curd, setting grain, drying, cheddaring, melting, forming a cheese head, salting, storing, transportation and sale of products. Cheese meets the requirements for organoleptic, physicochemical and microbiological indicators. The research results make it possible to recommend to farms the technology for the production of ‘Suluguni’ cheese with cheddaring and thermomechanical processing of the cheese mass.

Creep Behavior of Compact γ′-γ″ Coprecipitation Strengthened IN718-Variant Superalloy

The development of high-temperature heavy-duty turbine disk materials is critical for improving the overall efficiency of combined cycle power plants. An alloy development strategy to this end involves superalloys strengthened by ‘compact’ γ′-γ″ coprecipitates. Compact morphology of coprecipitates consists of a cuboidal γ′ precipitate such that γ″ discs coat its six {001} faces. The present work is an attempt to investigate the microstructure and creep behavior of a fully aged alloy exhibiting compact coprecipitates. We conducted heat treatments, detailed microstructural characterization, and creep testing at 1200 °F (649 °C) on an IN718-variant alloy. Our results indicate that aged IN718-27 samples exhibit a relatively uniform distribution of compact coprecipitates, irrespective of the cooling rate. However, the alloy ruptured at low strains during creep tests at 1200 °F (649 °C). At 100 ksi (689 MPa) load, the alloy fails around 0.1% strain, and 75 ksi (517 MPa) loading causes rupture at 0.3% strain. We also report extensive intergranular failure in all the tested samples, which is attributed to cracking along grain boundary precipitates. The results suggest that while the compact coprecipitates are indeed thermally stable during thermomechanical processing, the microstructure of the alloy needs to be optimized for better creep strength and rupture life.

A Scale-up Study on Chemical Segregation and the Effects on Tensile Properties in Two Medium Mn Steel Castings

Two ingots weighing 400 g and 5 kg with nominal compositions of Fe–8Mn–4Al–2Si–0.5C–0.07V–0.05Sn were produced to investigate the effect of processing variables on microstructure development. The larger casting has a cooling rate more representative of commercial production and provides an understanding of the potential challenges arising from casting-related segregation during efforts to scale up medium Mn steels, while the smaller casting has a high cooling rate and different segregation pattern. Sections from both ingots were homogenized at 1250 $$^{\circ} $$ ∘ C for various times to study the degree of chemical homogeneity and $$\delta $$ δ -ferrite dissolution. Within 2 hours, the Mn segregation range (max–min) decreased from 8.0 to 1.7 wt pct in the 400 g ingot and from 6.2 to 1.5 wt pct in the 5 kg ingot. Some $$\delta $$ δ -ferrite also remained untransformed after 2 hours in both ingots but with the 5 kg ingot showing nearly three times more than the 400 g ingot. Micress modeling was carried out, and good agreement was seen between predicted and measured segregation levels and distribution. After thermomechanical processing, it was found that the coarse untransformed $$\delta $$ δ -ferrite in the 5 kg ingot turned into coarse $$\delta $$ δ -ferrite stringers in the finished product, resulting in a slight decrease in yield strength. Nevertheless, rolled strips from both ingots showed $$>900$$ > 900 MPa yield strength, $$>1100$$ > 1100 MPa tensile strength, and $$>40$$ > 40 pct elongation with $$<10$$ < 10 pct difference in strength and no change in ductility when compared to a fully homogenized sample.