Caracterização tribológica de formação ferrífera bandada através do ensaio de esclerometria linear

Abstract

Rotary drilling is usually done with diamond-impregnated drill bits. These tools may present an unsatisfactory lifespan when working on a banded iron formation of Carajás-Brazil known as jaspilite, a complex material composed of alternated bands of silicates (jasper) and iron oxides (mostly hematite and goethite), besides quartz veins. The performance of these bits is linked to the interaction between diamond and jaspilite, which is poorly understood. The abrasive wear response of this tribosystem was investigated by a series of single-point scratch tests using Rockwell C, Vickers and Knoop diamond indenters as function of normal load (0.2-90 N). The effect of the distance between parallel scratches (ranging from 5 times the scratch width to total superimposition), scratching speed (0.01-1 mm/s) and environmental conditions (dry, distilled water and bentonite drilling fluid) on wear and friction behavior were studied with Vickers indenter. Severe wear by chipping and high friction (up to μ = 0.45) was dominant in all loads with Vickers indenter, at lower speeds, in all degrees of superimposition and lubricated conditions. Mild wear mechanisms (burnishing, ploughing and scale-like cracking) and lower friction (as low as μ = 0.06) were observed in tests with Rockwell and Knoop indenter, at high speeds and in iron oxides. Furthermore, the degree of superimposition had no effect on friction and wear mechanisms, although influenced wear rate