RESUMEN
The mechanical behavior, microstructures, as well as the crystallographic textures of the Ti57-Nb43 alloy were investigated on cylindrical specimens compressed at high temperatures, in the range of 700-1000 °C, and strain rates between 0.001 and 1.0 s-1. Hardening, followed by softening behaviors, were observed as a function of strain due to the occurrence of dynamic recrystallization/recovery in hot deformation. The modified five-parameter Voce-type equation described well the stress-strain curves, but, for the present alloy, it was also possible with only four parameters. A new two-variables polynomial function was employed on the four parameters that described well the flow curves as a direct function of temperature and strain rate. It permitted the reduction in the number of parameters and had the predictive capacity for the flow stress at any temperature, strain, and strain rate in the investigated range. The crystallographic textures were similar at all temperatures, with an increase in intensity from 900 °C. The textures could be characterized by a double <100> and <111> fiber and a unique component of (001) <110>, the latter inherited from the initial hot-rolling texture. Viscoplastic polycrystal self-consistent deformation modeling reproduced the measured textures showing that dynamic recrystallization did not alter the development of the deformation texture, only increased its intensity.
RESUMEN
The press and sinter method remains the standard among powder metallurgy processes for powdered stainless-steel materials. It delivers low cost, low oxidation rate, and adequate corrosion resistance. Furthermore, 17-4PH is a martensitic stainless-steel that is commonly used for high-strength and medium-ductility stainless steel parts. However, a few studies have investigated the press and sinter method for producing 17-4PH parts. This shortage is due to the high hardness (low compressibility) of 17-4PH powder. Thus, the main objective of this study is to evaluate the press and sinter method in terms of the manufacturing process, the influencing factors, and the theoretical basis of press and sinter methods in conjunction with metal injection molding technology for the production of 17-4PH parts. First, the literature and monographs are examined and summarized to cover the previous results, research progress, development trends, and applications of press and sinter method 17-4PH parts. Following the theoretical analysis, the practical investigation was conducted by producing parts with cold pressing from 800 to 1600â MPa, followed by sintering: the sintering temperature was 1200 °C for one hour under a protective vacuum atmosphere. ImageJ analysis was performed to measure the sinter density. The results showed an increase in relative sinter density from 84.43% to 96.43% for 800 and 1600â MPa, respectively, while the earlier results reached 93.47%. Overall, the press and sinter method enables the production of high-hardness 17-4PH parts with a high density, without using additives like lubricants, wax, or alloying elements.
RESUMEN
Nanocrystalline/amorphous powder was produced by ball milling of Ti50Cu25Ni20Sn5 (at.%) master alloy. Both laser diffraction particle size analyzer and scanning electron microscope (SEM) were used to monitor the changes in the particle size as well as in the shape of particles as a function of milling time. During ball milling, the average particle size decreased with milling time from >320 µm to ~38 µm after 180 min of milling. The deformation-induced hardening and phase transformation caused the hardness value to increase from 506 to 779 HV. X-ray diffraction (XRD) analysis was used to observe the changes in the phases/amorphous content as a function of milling time. The amount of amorphous fraction increased continuously until 120 min milling (36 wt % amorphous content). The interval of crystallite size was between 1 and 10 nm after 180 min of milling with 25 wt % amorphous fractions. Cubic Cu(Ni,Cu)Ti2 structure was transformed into the orthorhombic structure owing to the shear/stress, dislocations, and Cu substitution during the milling process.