In this work we consider the issue of influence of initial state of tool steel P6M5 surface on thickness and microhardness of hardened layer during ion nitriding in the glow discharge. It is established that the application of intense plastic deformation torsion before ion nitriding in the glow discharge increases the rate of nitrogen diffusion deep into the tool steel R6M5, and increases the thickness of the hardened layer by 2.5 times.
The present work is devoted to study of the oxidation behavior of two β-solidifying γ-TiAl alloys (Ti-43.5Al-4Nb-1Mo-0.1B (TNM alloy) and Ti-44Al-6(Nb, Zr, Hf)-0.15B (TNZ alloy) (at.%)). The as-cast alloys were subjected to upset forging and heat treatment that resulted in similar microstructures in both alloys. Plate-shaped samples were cut from the obtained workpieces, mechanically polished and subjected to oxidation exposure at 800°C (500 h). The samples during annealing were periodically removed from the furnace and weighed. After oxidation exposure the mass gain of the TNZ sample was found appreciably smaller than that of the TNM sample. The preliminary fluorination treatment in a diluted hydrofluoric acid (HF) provided a noticeable increase of the oxidation resistance in the case of the TNM alloy and a significant worsening of the oxidation resistance in the case of the TNZ alloy. At the same time, the non-fluorinated sample of the TNZ alloy showed near the same oxidation resistance as the TNM samples subjected to preliminary fluorination treatment. EDS analysis revealed the competitive formation of aluminum and titanium oxides on the surfaces of the oxidized TNM and TNZ samples. Predomination of the alumina formation contributed to higher oxidation resistance.
The work has been devoted to a study of the microstructure and mechanical properties of a novel heavily alloyed nickel base superalloy in cast and heat-treated (HT) and thermomechanically treated (TMT) conditions. The cast condition subjected to HT, including homogenization annealing, solid solution treatment and ageing, was characterized by a coarse γ grain size and uniformly distributed γ' precipitates with a size d γ' = 0.1-0.25 μm. TMT included unidirectional two-step forging in a thick-walled can made of stainless steel, which provided high quasi-hydrostatic pressure during forging, and intermediate recrystallization annealing at subsolvus temperatures. The TMT condition was aged. TMT led to the uniform development of recrystallization processes and the formation of predominantly recrystallized microstructure with a γ grain size d γ = 2 -50 μm. Non-recrystallized areas with up to 100 μm in size were also observed. After TMT and ageing, the microstructure contained mostly dispersed γ' precipitates with a size of d γ' = 0.1-0.3 μm. Tensile tests revealed that the strength properties in the TMT condition were by 20 -70 % higher than in the cast and HT condition. The TMT condition also showed an appreciably higher ductility than the HT condition. The following tensile properties were obtained at room temperature: σ UTS / σ 0.2 =1533 / 1083 MPa, δ =11 % after TMT and ageing, and σ UTS / σ 0.2 =1015 -1030 / 900 MPa, δ = 4.5 -5.2 % after HT. Higher tensile properties after TMT are explained by the γ grain refinement, the high γ' phase content, and the solid solution strengthening due to heavy alloying with substitution elements. At the same time, the presence of topologically close-packed phases probably reduced the mechanical properties.
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