ABSTRACT
In this study, thin ribbons of amorphous Mg72Zn27Pt1 and Mg72Zn27Ag1 alloys with potential use in biomedicine were analyzed in terms of the crystallization mechanism. Non-isothermal annealing in differential scanning calorimetry (DSC) with five heating rates and X-ray diffraction (XRD) during heating were performed. Characteristic temperatures were determined, and the relative crystalline volume fraction was estimated. The activation energies were calculated using the Kissinger method and the Avrami exponent using the Jeziorny-Avrami model. The addition of platinum and silver shifts the onset of crystallization towards higher temperatures, but Pt has a greater impact. In each case, Eg > Ex > Ep (activation energy of the glass transition, the onset of crystallization, and the peak, respectively), which indicates a greater energy barrier during glass transition than crystallization. The highest activation energy was observed for Mg72Zn27Pt1 due to the difference in the size of the atoms of all alloy components. The crystallization in Mg72Zn27Ag1 occurs faster than in Mg72Zn27Pt1, and the alloy with Pt has higher (temporary) thermal stability. The Avrami exponent (n) values oscillate in the range of 1.7-2.6, which can be interpreted as one- and two-dimensional crystal growth with a constant/decreasing nucleation rate during the process. Moreover, the lower the heating rate, the higher the nucleation rate. The values of n for Mg72Zn27Pt1 indicate a greater number of nuclei and grains than for Mg72Zn27Ag1. The XRD tests indicate the presence of α-Mg and Mg12Zn13 for both Mg72Zn27Pt1 and Mg72Zn27Ag1, but the contribution of the Mg12Zn13 phase is greater for Mg72Zn27Ag1.
ABSTRACT
The effect of Al and Ti additions on the microstructure and properties of CoNiFe alloys was studied in this paper. The investigations were conducted on four specially designed and produced arc furnace alloys (from 3 to 5 components, with medium to high entropy). Samples in various states were analyzed, i.e., as-cast, after homogenization, after solution heat treatment, and after solution heat treatment and aging. The obtained samples were characterized by: SEM observations, EDS, XRD, TEM analyses, and finally, hardness measurements. The solid solution strengthening coming from the addition of 5 at. pct. Al was negligible, while the effect from the 5 at. pct. of Ti addition was significant. The precipitation hardening effect related to the presence of the (CoNi)3Ti phase caused by the Ti addition is comparable with the total effect of the Al and Ti addition, which caused the precipitation of (NiCo)3AlTi.
ABSTRACT
The aim of the study was to analyze the crystallization kinetics of the Mg72Zn28 metallic glass alloy. The crystallization kinetics of Mg72Zn28 metallic glass were investigated by differential scanning calorimetry and X-ray diffraction. The phases formed during the crystallization process were identified as α-Mg and complex Mg12Zn13 phases. Activation energies for the glass transition temperature, crystallization onset, and peak were calculated based on the Kissinger model. The activation energy calculated from the Kissinger model was Eg = 176.91, Ex = 124.26, Ep1 = 117.49, and Ep2 = 114.48 kJ mol-1, respectively.
ABSTRACT
The modern power generation industry needs materials able to withstand severe conditions, such as high temperatures, steam pressure, and an aggressive environment, to create more electric power out of a decreasing amount of fuel. Therefore, new metallic materials are continuously being developed. In order to gain knowledge about modern materials, the investigation of high Cr and Ni austenitic steel oxidized in 100% steam at 700 °C for 500 h was performed. The morphology, the phase composition, and the chemical composition of the oxidation products were investigated through methods of advanced electron microscopy techniques. Moreover, precipitates present in bulk material were identified. The material developed a continuous and complex oxide scale, consisting of Fe2O3, Cr2O3, and spinel phases. Very fine MX, fine ε-Cu, and M23C6 precipitates were found in the bulk material. The creation of iron oxide is induced due to the coarse grain size of the material. Cr2O3 forms due to the internal oxidation process.
ABSTRACT
Alloy 709 was oxidized at 700 °C for 500 h in a steam environment. A microstructural analysis of the oxide scale is reported. Modern techniques of advanced electron microscopy were used to characterize the morphology of the oxide scale and recognize its single components. The material developed a complex, multilayered oxide scale. The outermost layer consisting of Fe2O3. Fe2NiO4 tI28 spinel was detected underneath. An internal oxidation zone is present in the innermost layer. High quality SEM-EDS maps give insight into a larger area of the oxide scale at a relatively low magnification.
ABSTRACT
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.
ABSTRACT
BACKGROUND: Recent years have seen a noticeable increase in the number of people experiencing total damage to the anterior cruciate ligament in the knee joint. The causes are many, but increased sporting activity among people who generally lead a hypokinetic lifestyle is regarded as the most important factor. Researchers are seeking to optimize the surgical treatment and rehabilitation. AIM OF THE STUDY: To evaluate the effectiveness of preoperative physiotherapy according to the Lysholm and Gillquist scale in patients scheduled for arthroscopic anterior cruciate ligament reconstruction. MATERIAL AND METHODS: The study involved a random sample of 30 patients with confirmed complete rupture of anterior cruciate ligament (ACL) qualified for surgical ACL reconstruction. Within this group, an experimental group consisted of 15 patients (mean age 41.0 ± 7 years) who attended physiotherapy before surgery based on recognized therapeutic models. A control group consisted of 15 patients (mean age 39.0 ± 9 years). The Lysholm and Gillquist 100-point scale was used for assessment. Student's t test, the Mann-Whitney U test and the Wilcoxon test were used for statistical analysis. The level of statistical significance was set at p < 0.05. RESULTS: The operated knee improved functionally in both the experimental and control group. In the experimental group, the difference was 20 points and was statistically significant at p = 0.000. In the control group, the difference was 6 points, which was also within the limit of statistical significance at p = 0.002. CONCLUSIONS: 1. Patients with total ACL rupture attending a pre-operative rehabilitation program led by a physiotherapist (experimental group) achieved greater improvement in functional status compared with the control group. 2. These results indicate a need to analyze the impact ofpreoperative rehabilitation on the final outcome of patients after complete ACL rupture.
