Microstructure and mechanical behavior of Al-xMg/5Al2O3 nanostructured composites

The effect of Mg content and milling time were investigated on the microstructure and microhardness values of Al-xMg/5Al2O3 (x = 0, 4, 8 and 12 wt %) nanostructured composite prepared via high energy milling technique. XRD results showed an acceleration of alloying process and formation of Al (Mg) ss by enhancing percentage of Mg element. Also, by increase in Mg percentage the grain size reduction was more considerable during milling treatment. Additionally, increment of the Mg content up to 12 wt%, causes the increase in micro-strain of the samples (from 0.31 to 0.82%). Increase in Mg concentration accelerates the mechanical milling process. According to SEM results a coaxial and circular morphology with a uniform distribution of powder particles has been formed. Up to 12 wt% (for each milling time), significant increase in microhardness (215 HV) was carried out due to solid solution hardening and crystallite refinement. From 10 to 15 h, a slight increase in microhardness up to 218 HV can be observed.

Solid Solution Strengthening of Mo, Re, Ta and W in Ni during High-Temperature Creep

Solid solution strengthening of the unordered γ matrix phase by alloying elements is of great importance during creep of Ni-based superalloys, particularly at high temperatures above 1000 °C. To study the role of different potent solutes, we have conducted creep experiments on binary Ni-2X alloys (X = Mo, Re, Ta, W) at 1000 °C, 1050 °C, and 1100 °C at a constant stress of 20 MPa. Compared to mechanical tests below 800 °C, where the size of the elements mostly determines the solid solution hardening contribution, the strengthening contribution of the different alloying elements above 1000 °C directly correlates with their diffusivity. Therefore, elements such as Ta that lead to strong solid solution hardening at low temperatures become less effective at higher temperatures and are exceeded by slower diffusing elements, such as Re.

Effect of Alloying Elements and Microstructure on the Dynamic Strain Aging Behavior of 1.25Cr-0.5Mo and 2.25Cr-1Mo Steels

The effect of alloying elements and microstructure on the dynamic strain aging (DSA) behavior of 1.25Cr-0.5Mo (P11, ASTM 335Gr.P11) and 2.25Cr-1Mo (P22, ASTM 335Gr.P22) steels was investigated. For both steels, different cooling conditions such as air-cooling (AC) and oil-quenching (OQ) were applied. Tensile tests were conducted in the temperature range of 20-450 ℃ and a strain rate in the range of 6 × 10-5- 6 × 10-3 s-1 for the steels with different cooling conditions. The P11AC steel showed serration behavior over a wider temperature range and exhibited higher ultimate tensile strength (UTS) than for the P22AC steel. This is attributed to the effects of alloying elements (Cr, Mo and Si) due to dissolved C, and the ferrite fraction on mechanical behavior. Meanwhile, the P11AC and P11OQ steels also showed different behaviors for DSA starting temperature, DSA temperature range, and serration type. The AC condition showed higher UTS from the interaction solid solution hardening (ISSH) effect due to substitutional Cr, Mo, and interstitial C elements. The calculated activation energy value (Q) for the P11 steel was around 94-103 kJ/mol-1, similar to that of ferritic steels, and it was higher for the P22 steel, with a Q value of 233 kJ/mol-1 from the ISSH effect.

Twin Roll Casting and Secondary Cooling of 6.0 wt.% Silicon Steel

Iron–silicon alloys with up to 6.5 wt.% Si offer an improvement of soft magnetic properties in electrical steels compared to conventional electrical steel grades. However, steels with high Si contents are very brittle and cannot be produced by cold rolling. In addition to solid solution hardening, it is assumed that the B2- and DO3-superlattice structures are responsible for the poor cold workability. In this work, two cast strips with 6.0 wt.% Si were successfully produced by the twin roll strip casting process and cooled differently by secondary cooling. The aim of the different cooling strategies was to suppress the formation of the embrittling superlattice structures and thus enable further processing by cold rolling. A comprehensive material characterization allows for the understanding of the influence of casting parameters and cooling strategies on segregation, microstructure and superlattice structure. The results show that both cooling strategies are not sufficient to prevent the formation of B2- and DO3-structures. Although the dark field images show a condition which is far from equilibrium, the achieved condition is not sufficient to ensure cold processing of the material.

Effect of Titanium Addition on the Structure, Microstructure, and Selected Mechanical Properties of As-Cast Zr-25Ta-xTi Alloys

Ti alloys are the most used metallic materials in the biomedical field due to their excellent biocompatibility associated with good corrosion resistance in body fluids and relatively low elastic modulus. However, the alloys used in the orthopedic area have an elastic modulus that is 2 to 4 times higher than that of human cortical bone. Searching for new alloys for biomedical applications and with low elastic modulus, zirconium gained prominence due to its attractive properties, especially its biocompatibility. The purpose of this paper is to present novel as-cast alloys of the Zr-25Ta-xTi system and analyze the influence of titanium on the structure, microstructure, microhardness, and elastic modulus of the alloys. The alloys were prepared using an arc-melting furnace. X-ray diffraction measurements and microscopy techniques were used to characterize the crystalline structure and microstructure. From structural and microstructural characterizations, it was observed that titanium acted as an α-stabilizing element since its increase in the precipitation of the orthorhombic α” phase, an intermediate phase from β to α phases, in the alloys. Regarding microhardness measurements, the alloys have higher hardness than pure zirconium due to solid solution hardening that detaches the Zr-25Ta alloy, which has a high hardness value of the precipitation of the ω phase. Among the studied alloys, the Zr-25Ta-25Ti alloy is highlighted, demonstrating the lowest result of modulus of elasticity, which is approximately 2 times higher than the human cortical bone, but many alloys used in the biomedical field, such as pure titanium, have elastic modulus values almost 3 times higher than that of human bone.

IMPACT OF COLD PLASTIC DEFORMATION AND THERMAL POST-TREATMENT ON THE PHYSICAL PROPERTIES OF COPPER BASED ALLOYS Al-BRONZE AND α-BRASS

The copper based alloys Al-bronze and α-brass containing each of 10wt% aluminum and zinc were prepared by casting. Afterwards, the specimens were cold-rolled with various percentages of deformation and the cold-rolled samples were aged subsequently at the varied time for four hours and temperatures ranging up to 500°C. Samples underwent characterizations by microhardness testing, electrical resistivity, optical properties, differential scanning calorimetry as well as microstructure analysis using an optical microscope. The results showed that the hardening of Cu-based alloys was taken place due to solid-solution hardening. Al addition accelerated the hardness through ageing due to the formation of various intermetallic copper aluminites into the aged alloy which was hard and brittle in nature. The resistivity decreased marginally through heat treatment due to the stage of stress relieving, recovery, precipitation coarsening as well as recrystallization and increased for arranging different intermetallics into the alloys. The microstructural study revealed that the cold rolled alloys content the different phases of elongated grain at the rolling direction. Meanwhile higher ageing temperatures at 500°C for one hour led to recrystallization and grain growth especially in pure copper and Cu-10Zn alloys.

Mechanisms of Solid-Solution Hardening of Single-Phase Cu-Al and Cu-Mn Alloys with a Mesh Dislocation Substructure

The dislocation structure and dislocation accumulation during deformation of polycrystalline FCC solid solutions of Cu-Al and Cu-Mn systems are studied by transmission diffraction electron microscopy. The Al content in Cu-Al alloys varies from 0.5 to 14 at.%. The Mn content in Cu-Mn alloys varies in the range of 0.4 ÷ 25 at.%. Alloys with a grain size in the range of 20 ÷ 240 µm are studied. The alloy samples are deformed by stretching at a rate of 2×10-2c-1 to failure at 293 K. The structure of samples deformed to various degrees of deformation is studied on foils using electron microscopes at an accelerating voltage of 125 kV. For each degree of deformation, the scalar dislocation density and its components are measured: statistically stored dislocations ρS and geometrically necessary dislocations ρG and some other parameters of the defective structure. The mechanisms and their contributions due to mesh and mesh-mesh dislocation substructures (DSS) are determined using the example of substructural and solid-solution hardening in polycrystalline Cu-Al and Cu-Mn alloys. The relative role of various mechanisms in the formation of the resistance to deformation of alloys at different grain sizes is determined. The role of the packaging defect energy on the value of solid-solution hardening for different grain sizes is revealed. The average scalar dislocation density is considered and determined along with its components: statistically stored dislocations ρS and geometrically necessary dislocations ρG. The dependences of the flow stress on the square root of the densities of geometrically necessary dislocations and the densities of statistically stored dislocations are found.

Effects of Zr and Sc additions on precipitation of α-Al(FeMn)Si dispersoids under various heat treatments in Al–Mg–Si AA6082 alloys

The present work investigated the influence of Zr and Sc on the evolution of α-Al(FeMn)Si dispersoids (“α-dispersoids") in Al–Mg–Si alloys. Both the individual addition of Zr and the combined additions of Sc and Zr increased the size but decreased the number density of the α-dispersoids, indicating the reduction in the formation of α-dispersoids. However, the reduction levels were the most significant when heat-treated at 350 °C in the alloy with both Sc and Zr and at 400 °C in the alloy with only Zr, which were likely related to the different interactions between intermediate B’ precipitates and α-dispersoids with the addition of Zr and Sc. Although the α-dispersoids were suppressed in the Zr/Sc-containing alloys, their microhardness was generally higher than the base alloy, which can be attributed to the strengthening contribution induced by Zr and Sc either from their solid solution hardening or the precipitation hardening of Al3Zr/Al3(Sc, Zr) dispersoids.

QUANTITATIVE ASSESSMENT OF THE YIELD STRESS OF FERRITE-PEARLITIC STEELS BY STRUCTURE PARAMETERS

In various sectors of the economy, requirements are imposed on the quality of metallurgical products. The event that improves the quality of metallurgical products - thermomechanical treatment (TMT). TMT allows reducing the specific consumption of steel, increasing the service life, reliability and durability of products, which is tantamount to an increase in the volume of finished metal products. The problem of applied materials science is the establishment of a quantitative relationship between the structure and properties of steels and alloys, it underlies the development and creation of new effective ways to improve the operational characteristics of metal products. In the production of long products, (TMT) is increasingly used, which is a combination of two methods of strengthening steels: deformational by plastic deformation and thermal by phase transformations. Revealing the features of the properties of heat-treated steels makes it possible to approach the solution of this problem. The main mechanisms of hardening are solid solution hardening by alloying with relatively cheap alloying elements (Mn, Si) and dislocation and precipitation hardening using hardening heat treatment and microalloying of steel with carbide and nitride-forming elements V (C, N). The article quantifies the approximate contribution of various strengthening mechanisms to the yield stress of carbon and low-alloy steels. For St5ps steel (hot-rolled state), the yield stress is given by solid-solution and grain-boundary hardening (37.4.0% and 28.6%), in low-alloy steel 16G2AF (36.7% and 27.1%), the role of dispersion hardening (28.0%).Thermomechanical treatment of steel grade St.5ps leads to an increase in the value of dislocation hardening up to 27.6% due to an increase in the density of dislocations and the retention of most of the dislocations in the rolled stock during accelerated cooling of hot-deformed austenite.