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Article
Publication date: 28 October 2019

Xiaoqing Ni, Liang Zhang, Wenheng Wu, Dexiang Zhu, Decheng Kong, Chaofang Dong and Guoliang Zhu

Laser melting deposition (LMD) is an advanced additive manufacturing (AM) technology without powder waste, and nickel-based alloys with different Nb contents were created one-time…

425

Abstract

Purpose

Laser melting deposition (LMD) is an advanced additive manufacturing (AM) technology without powder waste, and nickel-based alloys with different Nb contents were created one-time by adjusting the ratio of mixed powders via a dual-feed system. Here, the authors provide a systematic report on the effects of the Nb content on the microstructure, Laves phase segregation and mechanical properties of as-received LMD nickel-based alloys. The effects of the Nb content on the microstructure, precipitation evolution and mechanical properties of the subsequent heat-treated LMD samples are also discussed in this paper.

Design/methodology/approach

Thus, the present research aims to obtain a better understanding of the effect of Nb content on the microstructural and mechanical properties of the as-received LMD Inconel 718 alloys through high-throughput sample fabrication. The microstructures were characterized by scanning electron microscopy and energy-dispersive spectroscopy, electron back-scattered diffraction and transmission electron microscopy methods. The mechanical properties were obtained from compressive tests and nano-indentation tests. Electrochemical tests, including electrochemical impedance spectroscopy and potentiodynamic polarizations, were carried out to evaluate the durability of the Inconel 718 alloys. Results can provide a factual basis for future applications of the functionally graded by AM technology.

Findings

The grain size of the as-received LMD Inconel 718 alloys decreased with the Nb content. The Laves phase distribution at the macro level was relatively uniform and the Laves phase exhibited a 1.5-fold nano-hardness compared with the matrix. The strength improvement for the as-received LMD Inconel 718 alloys with Nb content was attributed to grain refinement and enhancement of the Laves phase in terms of both hardness and content. Meanwhile, the corrosion resistance increased with the increase of the Nb content, especially for the pitting potential, which was attributed to the optimization of carbide precipitates due to the strong affinity between niobium and carbon.

Originality/value

The results provide a factual basis for the Nb content effect in LMD nickel-based alloys, and this method can greatly promote the development of new materials. The authors believe that this study makes a significant contribution to the literature and is suitable for publication.

Details

Anti-Corrosion Methods and Materials, vol. 67 no. 1
Type: Research Article
ISSN: 0003-5599

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Article
Publication date: 21 December 2017

Marc Gürtler and Thomas Paulsen

Empirical publications on the time series modeling and forecasting of electricity prices vary widely regarding the conditions, and the findings make it difficult to generalize…

582

Abstract

Purpose

Empirical publications on the time series modeling and forecasting of electricity prices vary widely regarding the conditions, and the findings make it difficult to generalize results. Against this background, it is surprising that there is a lack of statistics-based literature reviews on the forecasting performance when comparing different models. The purpose of the present study is to fill this gap.

Design/methodology/approach

The authors conduct a comprehensive literature analysis from 2000 to 2015, covering 86 empirical studies on the time series modeling and forecasting of electricity spot prices. Various statistics are presented to characterize the empirical literature on electricity spot price modeling, and the forecasting performance of several model types and modifications is analyzed. The key issue of this study is to offer a comparison between different model types and modeling conditions regarding their forecasting performance, which is referred to as a quasi-meta-analysis, i.e. the analysis of analyses to achieve more general findings independent of the circumstances of single studies.

Findings

The authors find evidence that generalized autoregressive conditional heteroscedasticity models outperform their autoregressive–moving-average counterparts and that the consideration of explanatory variables improves forecasts.

Originality/value

To the best knowledge of the authors, this paper is the first to apply the methodology of meta-analyses in a literature review of the empirical forecasting literature on electricity spot markets.

Details

International Journal of Energy Sector Management, vol. 12 no. 1
Type: Research Article
ISSN: 1750-6220

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Article
Publication date: 20 December 2023

İdris Tuğrul Gülenç, Mingwen Bai, Ria L. Mitchell, Iain Todd and Beverley J. Inkson

Current methods for the preparation of composite powder feedstock for selective laser melting (SLM) rely on costly nanoparticles or yield inconsistent powder morphology. This…

249

Abstract

Purpose

Current methods for the preparation of composite powder feedstock for selective laser melting (SLM) rely on costly nanoparticles or yield inconsistent powder morphology. This study aims to develop a cost-effective Ti6Al4V-carbon feedstock, which preserves the parent Ti6Al4V particle’s flowability, and produces in situ TiC-reinforced Ti6Al4V composites with superior traits.

Design/methodology/approach

Ti6Al4V particles were directly mixed with graphite flakes in a planetary ball mill. This composite powder feedstock was used to manufacture in situ TiC-Ti6Al4V composites using various energy densities. Relative porosity, microstructure and hardness of the composites were evaluated for different SLM processing parameters.

Findings

Homogeneously carbon-coated Ti6Al4V particles were produced by direct mixing. After SLM processing, in situ grown 100–500 nm size TiC nanoparticles were distributed within the α-martensite Ti6Al4V matrix. The formation of TiC particles refines the Ti6Al4V β grain size. Relative density varied between 96.4% and 99.5% depending on the processing parameters. Hatch distance, exposure time and point distance were all effective on relative porosity change, whereas only exposure time and point distance were effective on hardness change.

Originality/value

This work introduces a novel, cost-effective powder feedstock preparation method for SLM manufacture of Ti6Al4V-TiC composites. The in situ SLM composites achieved in this study have high relative density values, well-dispersed TiC nanoparticles and increased hardness. In addition, the feedstock preparation method can be readily adapted for various matrix and reinforcement materials in future studies.

Details

Rapid Prototyping Journal, vol. 30 no. 2
Type: Research Article
ISSN: 1355-2546

Keywords

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