Modupeola Dada, Patricia Popoola, Ntombi Mathe, Sisa Pityana and Samson Adeosun
In this study, AlCoCrFeNi–Cu (Cu-based) and AlCoCrFeNi–Ti (Ti-based) high entropy alloys (HEAs) were fabricated using a direct blown powder technique via laser additive…
Abstract
Purpose
In this study, AlCoCrFeNi–Cu (Cu-based) and AlCoCrFeNi–Ti (Ti-based) high entropy alloys (HEAs) were fabricated using a direct blown powder technique via laser additive manufacturing on an A301 steel baseplate for aerospace applications. The purpose of this research is to investigate the electrical resistivity and oxidation behavior of the as-built copper (Cu)- and titanium (Ti)-based alloys and to understand the alloying effect, the HEAs core effects and the influence of laser parameters on the physical properties of the alloys.
Design/methodology/approach
The as-received AlCoCrFeNiCu and AlCoCrFeNiTi powders were used to fabricate HEA clads on an A301 steel baseplate preheated at 400°C using a 3 kW Rofin Sinar dY044 continuous-wave laser-deposition system fitted with a KUKA robotic arm. The deposits were sectioned using an electric cutting machine and prepared by standard metallographic methods to investigate the electrical and oxidation properties of the alloys.
Findings
The results showed that the laser power had the most influence on the physical properties of the alloys. The Ti-based alloy had better resistivity than the Cu-based alloy, whereas the Cu-based alloy had better oxidation residence than the Ti-based alloy which attributed to the compositional alloying effect (Cu, aluminum and nickel) and the orderliness of the lattice, which is significantly associated with the electron transportation; consequently, the more distorted the lattice, the easier the transportation of electrons and the better the properties of the HEAs.
Originality/value
It is evident from the studies that the composition of HEAs and the laser processing parameters are two significant factors that influence the physical properties of laser deposited HEAs for aerospace applications.
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Modupeola Dada, Patricia Popoola and Ntombi Mathe
This study aims to review the recent advancements in high entropy alloys (HEAs) called high entropy materials, including high entropy superalloys which are current potential…
Abstract
Purpose
This study aims to review the recent advancements in high entropy alloys (HEAs) called high entropy materials, including high entropy superalloys which are current potential alternatives to nickel superalloys for gas turbine applications. Understandings of the laser surface modification techniques of the HEA are discussed whilst future recommendations and remedies to manufacturing challenges via laser are outlined.
Design/methodology/approach
Materials used for high-pressure gas turbine engine applications must be able to withstand severe environmentally induced degradation, mechanical, thermal loads and general extreme conditions caused by hot corrosive gases, high-temperature oxidation and stress. Over the years, Nickel-based superalloys with elevated temperature rupture and creep resistance, excellent lifetime expectancy and solution strengthening L12 and γ´ precipitate used for turbine engine applications. However, the superalloy’s density, low creep strength, poor thermal conductivity, difficulty in machining and low fatigue resistance demands the innovation of new advanced materials.
Findings
HEAs is one of the most frequently investigated advanced materials, attributed to their configurational complexity and properties reported to exceed conventional materials. Thus, owing to their characteristic feature of the high entropy effect, several other materials have emerged to become potential solutions for several functional and structural applications in the aerospace industry. In a previous study, research contributions show that defects are associated with conventional manufacturing processes of HEAs; therefore, this study investigates new advances in the laser-based manufacturing and surface modification techniques of HEA.
Research limitations/implications
The AlxCoCrCuFeNi HEA system, particularly the Al0.5CoCrCuFeNi HEA has been extensively studied, attributed to its mechanical and physical properties exceeding that of pure metals for aerospace turbine engine applications and the advances in the fabrication and surface modification processes of the alloy was outlined to show the latest developments focusing only on laser-based manufacturing processing due to its many advantages.
Originality/value
It is evident that high entropy materials are a potential innovative alternative to conventional superalloys for turbine engine applications via laser additive manufacturing.
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Shahida Suleman, Safia Bibi, Muhammad Azam, Hassanudin Mohd Thas Thaker and Calvin W.H. Cheong
This research aims to systematically compare the impact of macro drivers on labor efficiency (LEFF) in high and low trade openness economies, employing the Solow model as the…
Abstract
Purpose
This research aims to systematically compare the impact of macro drivers on labor efficiency (LEFF) in high and low trade openness economies, employing the Solow model as the theoretical framework.
Design/methodology/approach
This study examines the influence of macro drivers on LEFF from 1995 to 2020, employing advanced panel regression methods such as stepwise regression (SR), fully modified ordinary least squares (FMOLS) and panel OLS. It utilizes Pedroni and Johansen co-integration tests to assess long-term dynamics and Granger causality tests to explore causal relationships between macro drivers and LEFF.
Findings
The results reveal both long-term and short-term relationships between LEFF and the macro drivers: gross capital formation (GCF), per capita income (PCI), foreign direct investment (FDI), trade openness (TOP) and gross national savings (GNS). The findings show that these macro drivers positively and significantly influence LEFF in both high and low TOP economies. Specifically, FDI, PCI and GNS have a more substantial positive impact on LEFF in low TOP economies, while GCF and TOP have a greater influence in high TOP economies. Furthermore, in high TOP economies, FDI, TOP and PCI exhibit a unidirectional relationship with LEFF, while GNS and GCF show a bidirectional relationship. In low TOP economies, all five macrodrivers exhibit bidirectional relationships with LEFF.
Research limitations/implications
This research focuses on countries with high and low TOP, limiting the generalizability of its findings to other economic systems due to the unique trade, institutional and governance frameworks of these two distinct groups.
Originality/value
To the best of the authors’ knowledge, this study is the first to compare the impact of theoretical macro drivers on LEFF across groups of countries differentiated by their degrees of TOP (high and low).