The Effect of Aluminium Addition on Solid Solution Strengthening in CoCrFeMnNi High Entropy Alloy: Experiment and Modelling

<p>The effect of aluminium addition to the Cantor alloy in the composition regime of 0.25-5 atomic percent on solid solution strengthening of single phase HEA was investigated using experiments and constitutive modeling. The continuous increase in yield and tensile strength without significant change in ductility is observed for the alloys characterized by almost similar grain sizes (~100 μm) with increasing aluminium content. The constitute modeling of the strengthening has been performed using traditional as well as recently developed models for solid solution strengthening. The constitutive modeling indicated significant contribution of solid solution strengthening due to addition of Al having relatively larger size (̴12%) than the size of elements in the Cantor alloy leading to severe local lattice distortion. The experimental yield strength could be best explained on the basis of large apparent distortion volume of Al atom acting as a stronger barrier to dislocation motion based on the Varvenne model. </p>

The Effect of Aluminium Addition on Solid Solution Strengthening in CoCrFeMnNi High Entropy Alloy: Experiment and Modelling

<p>The effect of aluminium addition to the Cantor alloy in the composition regime of 0.25-5 atomic percent on solid solution strengthening of single phase HEA was investigated using experiments and constitutive modeling. The continuous increase in yield and tensile strength without significant change in ductility is observed for the alloys characterized by almost similar grain sizes (~100 μm) with increasing aluminium content. The constitute modeling of the strengthening has been performed using traditional as well as recently developed models for solid solution strengthening. The constitutive modeling indicated significant contribution of solid solution strengthening due to addition of Al having relatively larger size (̴12%) than the size of elements in the Cantor alloy leading to severe local lattice distortion. The experimental yield strength could be best explained on the basis of large apparent distortion volume of Al atom acting as a stronger barrier to dislocation motion based on the Varvenne model. </p>

MICROSTRUCTURAL CHARACTERISTICS, MECHANICAL AND WEAR BEHAVIOUR OF ALUMINIUM-ALLOYED DUCTILE IRONS SUBJECTED TO TWO AUSTEMPERING PROCESSES

The effect of aluminium addition and austempering processes on the microstructures, mechanical and wear properties of rotary melting furnace processed ductile irons was investigated. Ductile irons containing 1−4 wt.% Al were produced and subjected to single and two-step austempering processes. Optical microscopy was used to characterize the graphite features and estimate the volume fraction of the matrix phases present, while the x-ray diffractogram was also carried out to analyse the samples. Mechanical and wear properties of the alloys were equally evaluated. From the results, it was observed that both the as-cast and austempered ductile iron microstructures contained nodular graphite, and the matrix structure for the as-cast ductile irons consisted predominantly of pearlite and ferrite, while that of the austempered grades, contained principally, ausferrite. The microstructure and intermetallic compound obtained played dominant role on the properties of the alloys. The aluminium addition and austempering processes had a significant influence on the mechanical properties and wear resistance of the alloys. The austempered ductile irons exhibited superior strength and wear resistance compared to the as-cast samples, albeit ductility values were lower in the composition group. Austempering increased the strength by over 100% while the addition of Al further enhanced the strength. The improved properties were linked to the refined microstructure, increased proportion of ausferrite phase and intermetallic compound formed. For all properties evaluated, the two-step austempering yielded better properties combination than the single step process. The rotary melting furnace processing adopted was found viable for ductile iron production.

A critical role of aluminium on austenite formation in high aluminium added steels

Novel alloys with high aluminium addition have been developed recently for the new concepts of δ-TRIP, δ-QP and some other high-aluminium low-density steels. The aluminium addition dramatically affects the thermodynamics and kinetics of the formation of austenite. In the present study, the effect of aluminium on the initial microstructure of ferrite and pearlite has been investigated. The equilibrium prediction of phase fraction by thermodynamics calculations is in accordance with the measured austenite fraction during isothermal at intercritical temperature range; both results strongly demonstrate a significant influence of aluminium addition on intercritical region. The isothermal transformation of high aluminium steel during intercritical annealing was delayed, which has an instruction for process design of the industrial continuous annealing and galvanization. The austenite formation during heating in intercritical region was also obviously affected by aluminium addition. The transformation kinetics simulation conducted by DICTRA simulation, as well as the experimental results of dilatometry, indicate a delayed austenite transformation during heating process.

Mechanical and Corrosion Behavior of Pure Aluminium Added Friction Stir Weld Joint of Aluminium Alloy

Friction stir welding (FSW) of AA2014 aluminium alloy was performed by sandwiching pure aluminium (Al) in the form of strip between the abutting surfaces. Mechanical and corrosion behavior of weld joint with and without pure aluminium addition was compared. Friction stir welding was carried out at rotational speed of 931 rpm and traverse speed of 41 mm/min. Pure aluminium strip of 1 mm thickness was used for incorporating Al in weld nugget zone. Microstructure analysis was carried out using optical microscope and FESEM with energy dispersive spectroscopy (EDS). Microhardness and tensile testing were performed on the weld joints. Corrosion behavior was investigated using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (Tafel) test. FESEM analysis was performed before and after corrosion test. Traces of pure aluminium strip were observed in the microstructure. The incorporated strip was found not to be uniformly distributed in the nugget zone. Pure aluminium addition reduced the extent of formation of the second phase particle in the nugget zone as compared to the normal FSW joint i.e. without Al addition. This metallurgical homogeneity resulted in better corrosion resistance of the Al added weld joint than the normal FSW joint.