Influence of Cold Rolling Process and Chemical Composition on the Mechanical Properties and Corrosion Behavior of Zr-Based Metallic Glasses

Cold rolling (CR) with thickness reduction of 10%, 30%, and 50% was applied to Zr50Cu44Al6 and Zr49.5Cu44Al6Nb0.5 metallic glassy ribbon samples. The XRD patterns showed the amorphousness of all samples after casting and CR processes. The SEM images indicated the formation of multiple shear bands (SBs) owing to plastic deformation during CR. However, the addition of 0.5 at% Nb to the alloy changed the SBs’ density and spacing characteristics. The characterization of free volume changes caused by CR was carried out by measuring the density of Archimedes. The micro-hardness of samples was studied by investigating SBs and free volume during plastic deformation. Alloy softening occurred due to the formation of free volume during CR. X-ray photoelectron spectroscopy (XPS) confirmed the presence of oxides ZrO2, CuOx, and AlOx on the surface of the ribbons. The anodic polarization curves of the cast and R50 samples in solutions of NaCl and Na2SO4 (0.5 M) were obtained using potentiodynamic polarization measurements. Compared to CR ribbons, melt-spun ribbons after casting showed better corrosion resistance with lower anodic current densities in Na2SO4 solution.

Nickel-Based Alloy Dry Milling Process Induced Material Softening Effect

Improving the cutting efficiency is the major factor for improving the processing of nickel-based alloys. The novelty of this research is the calibrated SiAlON ceramic tool dry milling nickel-based alloy process. Firstly, the nickel-based alloy dry milling process was analyzed through the finite element method, and the required milling force and temperature were deduced. Then, several dry milling experiments were conducted with the milling temperature, and the milling force was monitored. The change in cutting speeds was from 400 m/min to 700 m/min. Experimental results verified the reduction of the dry milling force hypothesized by the simulation. The experiment also indicated that with a cut depth of 0.3 mm, cut width of 6 mm, and feed per tooth of 0.03 mm/z, when milling speed exceeded 527.52 m/min, the milling force began to decrease, and the milling temperature exceeded the nickel-based alloy softening temperature. This indicated that easy cutting could be realized under high-speed dry milling conditions. The interpolation curve about average temperature and average milling forces showed similarity to the tensile strength reduction with the rise of temperature.

Design of Wear-Resistant Diecast AlSi9Cu3(Fe) Alloys for High-Temperature Components

Type AlSi9Cu3(Fe) alloy has been modified by alloying with iron, manganese, and chromium elements to develop wear-resistant diecast hypoeutectic Al–Si–Cu alloys that can be applied for high-temperature applications. Several alloys have been produced by varying iron, manganese, and chromium levels (0.80, 1.00, 1.20 wt.% for Fe; 0.25, 0.40, 0.55 wt.% for Mn, and 0.06, 0.10 wt.% for Cr). Brinell hardness measurements and pin-on-disk wear tests have been conducted from room temperature up to 200 °C. The microstructural changes that occurred with the different alloying levels have been quantitatively examined by metallographic and image analysis techniques. The results showed how the increasing content of the Fe, Mn, and Cr promoted the precipitation of both primary and secondary Fe-enriched particles, mainly with polyhedral, blocky, and star-like morphologies. These compounds showed high hardness that is not affected by chemical composition and morphology variation. At high temperatures, the diecast alloys always showed lower average hardness and wear resistance, especially at 200 °C; however, a greater amount of Fe-rich particles can compensate the alloy softening.

Microstructure and calorimetric behavior of laser welded open cell foams in CuZnAl shape memory alloy

Cellular shape memory alloys (SMAs) are very promising smart materials able to combine functional properties of the material with lightness, stiffness, and damping capacity of the cellular structure. Their processing with low modification of the material properties remains an open question. In this work, the laser weldability of CuZnAl SMA in the form of open cell foams was studied. The cellular structure was proved to be successfully welded in lap joint configuration by using a thin plate of the same alloy. Softening was seen in the welded bead in all the investigated ranges of process speed as well as a double stage heat affected zone was identified due to different microstructures; the martensitic transformation was shifted to higher temperatures and the corresponding peaks were sharper with respect to the base material due to the rapid solidification of the material. Anyways, no compositional variations were detected in the joints.

Thermal Stability of Al-Si-Cu-Mg Cast Alloys Modified with Transition Metals Zr, V and Ti

The hypoeutectic Al-7Si-1Cu-0.5Mg (wt%) alloy was modified with micro-additions of Zr, V and Ti in order to improve its thermal stability. As revealed by a number of experimental techniques, Cu and Mg rich phases along with the eutectic Si dissolved in the temperature range from 300 to 500°C. At the same time, the (AlSi)x(TiVZr) phases containing transition metals were present up to 696–705°C. During isochronal aging, the modified alloy exerted different aging characteristics than the reference A380 grade with a higher peak hardness and a lower temperature of alloy softening. Micro-additions of Ti, V and Zr positively affected the alloy strength during testing both in as-cast state and after T6 heat treatment. Improvements in tensile and compressive strength as compared to the reference alloy were preserved up to temperatures over 200 °C with more positive effect seen for the T6 state.

Research on Law and Mechanism of Hydrogen Induced Softening in Ti6Al4V Alloy in the Temperature Range 400 °C to 1010 °C

The law and mechanism of hydrogen induced softening in Ti6Al4V alloy in the temperature range 400 °C to 1010 °C are researched by lots of isothermal hot compression experiment in this paper. The relationship between σh (the true stress when the test is compressed to half of its original height) and CH (hydrogen content) is investigated to describe the law. The results show that, Between 400 °C and 450 °C, the plasticity increases at first, and then decreases and the strength is almost changeless with the CH rising. Between 480 °C and 950 °C, the strength decreases at first, and then increases with the CH rising. In α+β phase region, the strength decreases with the CH rising. In β phase region, the strength increases with the CH rising. Hydrogenation induced α phase high temperature softening and hydrogenation promoting α→β phase transition are the main reasons for hydrogen induced titanium alloy softening. Hydrogenation induced β phase solution strengthening is the reason for hydrogen induced titanium alloy strengthening. And the relationship between furnace temperature and vacuum is investigated during dehydrogenation heat treatment.

Modelling Age Hardening CuCr1Zr Electrode Alloy Softening during Resistance Spot Welding

High strength zinc-coated steels are used for automotive applications when high corrosion resistance and weight reduction are required. Resistance spot welding is the main method to assembly auto body. Steel sheets are held together under pressure exerted by copper alloy electrodes which concentrate welding current and clamp the sheets together. But welding of high strength coated steels reduces the electrode life. Even if electrode deterioration is a well-known problem, the understanding and modelling of the complex deterioration modes at different regions of the electrode is still limited. Developing a comprehensive thermo-electrical-metallurgical-mechanical model that describes the sequential deterioration is thus lacking. This work is a preliminary study which specifically addresses microstructural evolution modelling in age hardened CuCr1Zr electrode alloy. Evolution of precipitation is simulated using two models: a Johnson-Mehl-Avrami-Kologoromov model and the Myhr and Grong model. In both cases a calibration procedure based on hardness data was involved. Short isothermal heat treatments were used to develop a ‘master curve’ which captures the precipitate evolution. Preliminary results about the comparison of the two models are presented.

Influence of solute additions on the fracture behaviour of Armco iron

The influence of solutes, namely cobalt, molybdenum, nickel and silicon, on the deformation and fracture behaviour of Armco iron has been studied. The J -integral method was used for the measurement of ductile initiation fracture toughness J IC . Although cobalt is seen to enhance significantly J IC of the starting material (Armco iron), molybdenum, nickel and silicon are observed to have a deleterious effect. The increase in J IC with cobalt addition can be understood in terms of the enhanced strain hardening exponent, which is known to have a bearing on the plastic zone size around the crack tip and on micromechanisms of crack initiation. The large decrease in J IC with silicon and higher molybdenum concentration is explained on the basis of a change in fracture mode from ductile to cleavage as a result of stress concentration ahead of the crack tip reaching the cleavage fracture stress. The loss in fracture toughness with nickel addition is attributed to sulphur segregation at grain boundaries which results in pockets of intergranular fracture. Cobalt addition leads to alloy softening. Through secondary ion mass spectroscopy (SIMS), experimental evidence has been obtained for the first time for the suggestion that the ‘scavenging’ of interstitials leads to alloy softening. It was observed through yield stress dependence on grain size that the Hall–Petch constants σ 0 and k y substantiate SIMS observations.