Load-dependence of the measured hardness of Ti(C,N)-based cermets

doi:10.1016/S0921-5093(00)01845-1

Materials Science and Engineering: A

Volume 303, Issues 1–2, 15 May 2001, Pages 179-186

https://doi.org/10.1016/S0921-5093(00)01845-1 Get rights and content

Abstract

The Vickers hardnesses of a series of Ti(C,N)-based cermets were measured in the indentation load range from 1.47 to 40.67 N. It was found that the examined materials exhibit a reversed indentation size effect, i.e. the measured hardness increases with increasing indentation load. Both Meyer's law and the energy balance model can not provide a proper description for the observed experimental phenomena, while the polynomial series representation can describe the experimental data very well. A possible explanation for the cause of the observed reverse indentation size effect was also proposed.

Introduction

Ti(C,N)-based cermets have been successfully introduced in the metal cutting industry and are now competing, in prices and properties, with conventional hard metals at high cutting speeds and in finishing and milling operations [1], [2]. Literature concerning the processes and properties of Ti(C,N)-based cermets frequently reported the measured indentation hardness, a key parameter for characterizing the cutting performance of cutting tool materials. However, a complete description of the hardness characteristics of these cermets seems to be still lacking. It has been well known that the indentation hardness, which is traditionally defined as the ratio of the indentation test load to the contact (or projected) area of the resultant indentation impression, usually decreases as the test load increases. Such a phenomenon is sometimes referred to as the indentation size effect (ISE) [3]. Because of the existence of the ISE, it is often very difficult to make any quantitative comparisons between the hardness data for a given cermet measured at different load levels by different authors. Furthermore, any close examination on the connection between the hardness and the chemical composition and the microstructural characteristics of the materials is also impossible if the measured hardness numbers for different materials have not been corrected to be load-independent. Unfortunately, to our knowledge, there has been little effort devoted to the ISE in Ti(C,N)-based cermets.

During the past two decades, the source of the ISE observed in brittle materials has been extensively studied [4], [5], [6], [7], [8]. As a result, several empirical or semi-empirical equations have also been established to quantitatively describe the ISE. In the present work, the applicability of these equations to the description of the hardness characteristics of Ti(C,N)-based cermets based on data obtained from Vickers hardness measurements on a series of Ti(C,N)-based cermets were examined.

Section snippets

Experimental

The cermets chosen for the present study were composed of 90 wt.% Ti(C,N) ceramic hard phase and a (5 wt.% Mo+5 wt.% Ni) metal binding phase. Table 1 gives the sintering condition, average size of Ti(C,N) grains and the Rockwell hardness (HRC) for each test sample.

The test samples were received in the form of disks, about 22 mm in diameter and 4 mm in thickness, with flat, parallel-machined surfaces. One of the two surfaces of each sample was polished carefully with successively finer diamond

Experimental phenomena

In Fig. 1, the measured Vickers hardness, H_V, was plotted as a function of indentation load, P, for each sample. As can be seen, the measured Vickers hardness for each sample increases significantly with indentation load at low load region and then tends to invariable as indentation load increases further. Such phenomena are rather different from those reported for most brittle ceramics, whose hardnesses were found to decrease with increasing load [6], [7], and called hereafter the reversed

Summary and conclusions

The load-dependence of the measured Vickers hardness of Ti(C,N)-based cermets was examined in the present study. Particular emphasis was paid to the applicabilities of some previously proposed empirical or semi-empirical equations to the description of the experimental data. The following conclusions were deduced.

Unlike many other brittle ceramics, the Ti(C,N)-based cermets exhibit a reverse indentation size effect. That is, the measured hardness increases with increasing indentation load in

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Citation Excerpt :
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Load-dependence of the measured hardness of Ti(C,N)-based cermets

Abstract

Introduction

Section snippets

Experimental

Experimental phenomena

Summary and conclusions

Mater. Sci. Eng.

Int. J. Refract. Met. Hard Mater.

J. Eur. Ceram. Soc.

J. Mater. Sci.

Mater. Sci. Eng.

Mater. Lett.

Phys. Status Solidi

J. Mater. Sci.

J. Mater. Sci.

J. Mater. Sci.

J. Am. Ceram. Soc.

Indian J. Technol.