Phenomenological Models and Peculiarities of Evaluating Fatigue Life of Aluminum Alloys Subjected to Dynamic Non-Equilibrium Processes

Physical-mechanical models for predicting the fatigue life of aluminum alloys D16ChATW and 2024-T351 are proposed and tested. Damage accumulation patterns are established for these alloys in the initial state and after dynamic non-equilibrium processes (DNP) of different intensity that occur at maximum cycle stresses σmax from 340 to 440 MPa, cycle asymmetry coefficients R = 0.1 and load frequency f = 110 Hz. The main model parameters are the initial alloy hardness HV and the limiting parameters of scatter of hardness values m. These parameters are evaluated in the process of cyclic loading with fixed maximum stresses of the cycles. Relative values me are also considered. For the alloys in the initial state, the proposed models are shown to be in good agreement with the experimental results. Conversely, structural changes taking place in alloys after DNP complicate the prediction of their fatigue life.

Studies on Tribological and Statistical Modeling for Al/ZrO2 MMC’s

In recent era early growth and remarkable development with regards of composite materials has become a need of designing area on account of consideration to the drawbacks over conventional materials in improving material properties which includes viz, stiffness, density, toughness, and strength.This research focuses on utilizing the stir casting method of forming better metal matrix composite by using ZrO2 as reinforcing material thereby developing a composite material.Current study investigates Al357 alloy is fortified with different percentage of ZrO2 (3%, 5% and 7%) is concocted by the stir casting and studied for a microstructure, mechanical and the statistical modelling of wear analysis. Wear tracks of the as-cast alloy and its composites were examined using SEM. From the results it was concluded that compared to as-cast alloy A357/ 7 % ZrO2 displayed better properties compared followed by 5% and 3% composites. Keywords: MMC’S; ZrO2; Aluminium 357 alloy; Hardness test; Statistical Analysis.

Influence of the chemical composition on the hardness of defibrator plate segments

Influence of the chemical composition on the hardness of defibrator plate segments. The paper presents the results of the hardness measurements of the material of defibrator plate segments, in connection with their chemical composition. The investigations of the chemical composition were performed using Energy Dispersive X-ray Spectroscopy (EDS). The hardness was measured using the Rockwell method. The increased number of the alloy components leads to an increase in hardness by approx. 3%, in comparison with the normalized L210H21S cast steel. Changes of the chemical composition and increase in the number of alloy components are ineffective from the viewpoint of the alloy hardness.

Morphological Evolutions of Ni-Rich Phases in Al-Si Piston Alloys during 250–400 °C Thermal Exposure Processes

The thermal stability of the Al-Si alloys during the thermal exposure process from 250 °C to 400 °C was systematically investigated. The relationships between the morphological evolution and the mechanical changes of the alloys were determined through the Vickers hardness test and materials characterization method. Initially, the alloys exhibited similar thermal degradation behavior. For example, the exposure process of the alloy at 300 °C can be divided into two stages according to the changes of the alloy hardness and the matrix micro-hardness. In detail, the first stage (0–2 h) exhibited a severe reduction of the alloy hardness while the second stage showed a more leveled hardness during the following 98 h. There are three identified morphological characteristics of Ni-rich phases in the alloy. Furthermore, the differences in both composition and the micro-hardness between these Ni-rich phases were confirmed. The underlying relationships between the morphological transformation of the Ni-rich phases and hardness fluctuation in the alloy were correlated and elucidated. The observed alloy hardness increase when the exposure temperature was 400 °C was unexpected. This behavior was explained from the perspectives of both Ni-rich phases evolution and dispersoid formation.

On The Microstructures and Hardness of The Nb-24Ti-18Si-5Al-5Cr-5Ge and Nb-24Ti-18Si-5Al-5Cr-5Ge-5Hf (at.%) Silicide Based Alloys

The microstructures and hardness of the as cast and heat treated (1400 °C/100 h) alloys Nb-24Ti-18Si-5Ge-5Cr-5Al (ZF6) and Nb-24Ti-18Si-5Ge-5Cr-5Al-5Hf (ZF9) were studied. Both alloys were compared with refractory metal bcc solid solution + intermetallic High Entropy Alloys (HEAs). There was macrosegregation of Si, Ti, Cr and Al in both alloys. The roles of Ge and Hf on macrosegregation are discussed. In both alloys the primary phase was the βNb5Si3. In the as cast alloy ZF6 the Nbss, βNb5Si3 and C14-NbCr2 Laves phase and Nbss + βNb5Si3 eutectic were formed. The microstructure of the as cast alloy ZF9 consisted of Nbss, βNb5Si3, γNb5Si3 and C14-NbCr2 Laves phase. The heat-treated microstructures of the alloys ZF6 and ZF9 consisted of Nbss, βNb5Si3 and αNb5Si3 and Nbss, βNb5Si3, αNb5Si3 and γNb5Si3, respectively. The surfaces of both alloys were contaminated by oxygen where TiO2 and HfO2 formed respectively in the alloys ZF6 and ZF9. Alloying with Hf increased the lattice parameter of Nbss and decreased the hardness of ZF9 and Nb5Si3. The roles of alloying additions on the hardness of the Nbss and Nb5Si3 and relationships between alloy hardness and alloy parameters VEC (valence electron concentration), δ (related to atomic size) and Δχ (related to electronegativity) were discussed.

Analisis Kekerasan Permukaan Titanium-6A1-4V Pada Proses EDM Sinking Dengan Aplikasi Response Surdace Methodology (RSM)

This study looked at the effect of severed EDM process parameters on the optimum value of titanium alloy hardness. this study uses Design Expert 9.0 software to help develop an experimental plan of response surface method models and CCD. The machine used is Hitachi Electrical Discharge Machining (EDM) brand with Series H-DS02-S. Material used titanium 6Al-4V. Electrode used copper (Cu). The process parameters used are Current (A), On time (μs) and Off time (μs). Coolant fluid using Hydroseal 63H. The results of data processing there are 20 experiments. This research shows optimum machining condition for hardness (HV) is 322. Analysis of variance (Anova) shows the value of F arithmetic is 3,94, MSE is 0,022 and p (0,0794). The increase of current and on-time values ​​gives a great influence on surface roughness. The increase of Off time value does not give significant effect to the roughness. The next research will be done with 5 (five) process parameters, Current, On time, Off time, Machining Voltage and Servo feed.

Effects of Mg Addition and Pre-Aging on the Age-Hardening Behavior in Al-Mg-Si

Two types of nanoclusters, Cluster (1) and Cluster (2), formed at around room temperature and 100 °C, respectively, affect the age-hardening behavior in Al-Mg-Si alloys. Formation of Cluster (1) during natural aging (NA) is more accelerated in the high-Mg (9M10S) alloy than in the low-Mg (3M10S) alloy. Hardness at the early stage of two-step aging at 170 °C is not increased for the natural aging samples. On the other hand, hardness is directly increased for the pre-aged (PA) specimens. Furthermore, the formation of Cluster (1) during natural aging is suppressed by the formation of Cluster (2) during pre-aging at 100 °C. To understand the effects of heat treatment histories and Mg contents on the microstructure, transmission electron microscopy (TEM) was utilized. All the images were obtained at (001) plane, and peak aged samples with different heat treatments were used. Lower number density of precipitates is confirmed for the natural aging samples compared with the single-aged and pre-aged specimens. A higher number density of precipitates is confirmed for 9M10S in comparison to 3M10S. Hardness results correspond well to the TEM images.

Influence of σ Phase on the Allotropic Transformation of the Matrix in Co-Re-Cr-Based Alloys with Ni Addition

Co-Re-Cr alloys are being developed for high-temperature application in gas turbines. In these alloys, the Cr2Re3-based σ phase is stable when the Cr content is higher than 20 atomic %. The addition of Ni is being studied to partially substitute Cr, which aims to suppress σ formation without sacrificing the benefit of Cr in the oxidation resistance of the alloy. The microstructure of the alloys with varying Cr (18–23%) and Ni (8–25%) was investigated by electron microscopy in the present study, primarily to look into the stability of the σ phase and its influence on the Co matrix phase transformation. The σ phase is mainly found in two morphologies in these alloys, where at high temperature only blocky σ phase is present at grain boundaries but cellular σ is formed through a discontinuous precipitation within the grains at lower heat treatment temperatures. The presence of fine cellular σ phase influences the alloy hardness. Moreover, the σ precipitation, which depletes the matrix in Re, also influences the allotropic transformation of the Co matrix.