Elsevier

Materials Letters

Volume 273, 15 August 2020, 127944
Materials Letters

Effect of hot pressing and hot isostatic pressing on the microstructure, hardness, and wear behavior of nickel

https://doi.org/10.1016/j.matlet.2020.127944Get rights and content

Highlights

  • Microstructure, mechanical properties and wear behavior of Nickel were investigated.

  • Microstructural differences of the Nickel obtained by hot pressing and hot isostatic pressing were established.

  • The hardness and elastic moduli for all samples were obtained.

  • The influence of the consolidation process of nickel on COF was determined.

Abstract

Nanocrystalline Ni (Ninc) obtained by mechanical milling may present improved mechanical properties paired with high abrasion resistance. Different sintering processes were used to consolidate Nanocrystaline Ni: hot pressed (HP) and hot-isostatic pressed (HIP). The microstructure, mechanical properties, and tribological were evaluated to compare the processes. X-ray diffraction patterns showed that HIP-consolidated specimens had larger crystallite sizes and 37% less microstrain when compared to the HP specimens. The nanohardness of the HIP specimens was also carried out and it was 50% lower than that of HP specimens, whereas its coefficient of friction found was 25% higher. These results show the advantages of the HP process over the HIP since the high pressure. The low sintering temperature of HP inhibited the grain growth, which leads excellent mechanical and tribological properties of Ni.

Introduction

Nickel is widely used in powder metallurgy as an alloying element for sintered steels [1], [2], in the form of self-lubricating nickel composites [3] and nickel-based super alloys [4], amongst other applications [5], [6]. Nanocrystalline nickel and Ni-based coatings have been proven to have an excellent tribological behavior in pin-on-disk and scratch tests [7], [8]. It has been found that the coefficient of friction in these coatings decrease with crystallite size due to the short range deformation processes undergone by Ninc during tribological testing when compared to the energy consuming large scale plastic deformation process present in conventional microcrystalline Nickel [9].

However, up to this point the feasibility of using Ni(nc) is limited to coatings, as bulk-processing techniques does not usually allow the obtaining of nanocrystalline Ni with complex geometries due to grain growth during processing [10]. Powder metallurgy (PM) allows obtaining bulk materials with complex geometries while using low temperatures. Hot pressing (HP) is a PM effective technique which allows obtaining fine grained materials through rapid heating of powders under moderate loads [11]. Another interesting technique for densification of PM materials, is Hot Isostatic Pressing (HIP) which consist in placing a preform into a high pressure chamber, where high pressure and temperature is applied through gas, allowing to obtain almost completely dense parts [12].

The aim of this study is to obtain nanocrystalline Ni trough high-energy milling and then sintering it using the HP and HIP techniques in order to characterize their microstructure, mechanical properties, and tribological behavior.

Section snippets

Experimental

Ni powders (99% at., <10 µm, Merck) were mechanically milled under argon atmosphere using a SPEX 8000D high-energy mill. The milling was conducted using ball/powder ratio was 10:1, Stearic acid being added as a controlling agent, and the milling time of five hours. The resulting powders were sintered using Uni-axial Hot Pressing (HP) at a pressure of 900 MPa at 300 °C and 2 min of holding time [13], and also using Hot Isostatic Pressing (HIP) at a pressure of 150 MPa and 900 °C for 1 h.

The

Results and discussion

Fig. 1a displays the X-ray diffraction patterns of nickel before and after the different consolidation methods. The milling process produced a decrease in the crystallite size, as well as an increased microstrain, which is reflected in the broadening of the peaks than the as-received sample. After sintering, the crystallite size increases and the number of crystalline defects is reduced, this produces narrow and slightly more intense peaks. Furthermore, Ni_HP presents small amounts of

Conclusions

Ninc samples were prepared by high-energy milling, hot pressing, and hot isostatic pressing. The HIP samples were more densified than the HP samples; however, the hardness and elastic modulus were higher for the HP samples due to smaller crystallite sizes and higher microstrain. The higher hardness of the HP specimens translated into lower COF and wear after the scratch tests. The results of this study show that high-energy milling, combined with hot pressing, is a powerful method for producing

CRediT authorship contribution statement

Carola Martínez: Conceptualization, Methodology, Validation, Investigation, Writing - review & editing, Visualization. Francisco Briones: Methodology, Validation, Writing - original draft. Claudio Aguilar: . Nicolás Araya: Validation, Writing - original draft. Iñigo Iturriza: Provision of resources for fabrication of nickel samples. Izabel Machado:Auxiliary edition of the manuscript. Paula Rojas:Resources, Auxiliary edition of the manuscript.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was financial support by FONDECYT (Grant 3140207; 1130475) and PhD student, CNPq and BNDES.

References (19)

  • L. Rapoport et al.

    Tribol. Int.

    (2002)
  • X. Zhao et al.

    Int. J. Hydrogen Energy

    (2008)
  • M. Fukushima et al.

    Mater. Lett.

    (2015)
  • P. Narasimman et al.

    Wear

    (2012)
  • N.P. Wasekar et al.

    Wear

    (2012)
  • M.A. Bousnina et al.

    J. Alloy. Compd.

    (2010)
  • S.H. Chang et al.

    Int. J. Refract Metal Hard Mater.

    (2012)
  • T. Yildiz et al.

    J. Alloy. Compd.

    (2018)
  • G. Williamson et al.

    Acta Metall.

    (1953)
There are more references available in the full text version of this article.

Cited by (0)

View full text