Depth-sensing Measurements Research Articles

Impact of Micro-Indentation on Hardness and Indentation Depth of Ni-Cr Super Alloys

ABSTRACT A material’s (metal, composite, polymer, etc.) behaviour is greatly influenced by the indentation hardness and elastic modulus during any operation (sliding, fretting, turning, etc.). To measure the micromechanical properties of surfaces, subsurfaces and coated thin layers of materials, depth-sensing measurement indentation techniques are most commonly used. The present study aims to develop a compressive model to investigate the influence of indentation parameters on the indentation hardness and indentation depth of Ni-Cr superalloy during indentation experiments. Experiments were conducted based on model L18 (21*32) full factorial design with a mixed orthogonal array using a microhardness tester. The experiments revealed that indentation hardness values show a normal indentation size effect with respect to indentation load. Indentation depth values increase with the increase in indentation load. Taguchi's approach and the regression analysis were used to model the indentation hardness and indentation depth with respect to indentation parameters. Analysis of variance was employed to check the effect of input parameters on performance outputs. The experimental and predicted values show a good degree of proximity. However, indentation load (79.22% and 52.34%) was found to be the most dominant parameter affecting indentation hardness and indentation depth, respectively, followed by dwell time.

Determination of mechanical properties by instrumented indentation

The paper reviews the current state of the depth-sensing indentation (sometimes called nanoindentation), where the information on material behaviour and properties is obtained from the indenter load and depth, measured continuously during loading and unloading. It is shown how the contact parameters and principal characteristics are determined using pointed or spherical indenters. Indentation tests can be used for the measurement of hardness and elastic modulus, and also of the yield stress and for the construction of stress–strain diagrams, for the determination of the work of indentation and its components. Most devices use monotonic loading and unloading, but some also enable measurement under a small harmonic signal added to the basic monotonously increasing load. This makes possible continuous measurement of contact stiffness and the study of dynamic properties and the determination of properties of coatings. One section is devoted to the measurement on viscoelastic-plastic materials, where the delayed deforming must be considered during the measurement as well as in data evaluation. Instrumented indentation can also be used for the study of creep under high temperatures. The paper also discusses the errors arising in depth-sensing measurements and informs briefly about some other possibilities of the method.

Universalhärte

Legitimate, practicable, expandable. The convenient procedure of deriving hardness from depth-sensing measurement is well compatible with conventional hardness concepts, despite of some peculiarities. By applying two independent and largely non-arbitrary corrections the results derived from the load vs. depth curves can be made more useful: The correction with respect to resilience provides compatibility with Vickers hardness. Deriving hardness without referring to the cumbersome zero depth point suppresses the load dependence.