Application

Scratch Testing

Related to:

Application Overview

Scratch testing is one of the oldest methods for assessing hardness and is also among the least well-understood. This is primarily due to the complexity of the stress states at the tip. However, perhaps all that is needed is a more comprehensive view.

With the use of new nanoindentation tools, it is now possible to clearly visualize deformation processes during scratch testing, while simultaneously measuring depth, normal and lateral forces, coefficients of friction, and acquiring pre- and post-scans of surface topology. This advancement brings scratch testing firmly into the toolkit of the modern materials scientist.

<p>Scanning Electron Microscope and surface topology images of a scratch test performed on aluminium.</p>

<p>Graphs displaying scratch depth, residual depth, coefficient of friction, and forces recorded during a scratch test performed on aluminium.</p>

<p>Scratch test topography providing quantitative data on material hardness and wear resistance.</p>

Application Examples

Tribological Assessment

Tribology and Chip Formation

Scratch testing plays a crucial role in understanding wear mechanisms in tribology, specifically abrasion and erosion processes, as well as offering insight into chip formation during machining. Through observation of various materials deformation behaviors (e.g. plastic slip, grain rotation and pile-up, shear banding, extrusion, and cracking), we gain valuable technical knowledge.

In this application example, an aluminum single crystal (SX) demonstrates smooth deformation, highlighting the importance of slip planes, while ultra-fine grained (UFG) aluminum exhibits a textured chip, indicating the movement of individual grains. Additionally, bulk metallic glass (BMG) and Al-Cu eutectic alloy samples display unique deformation patterns, like serrated flow and local scratch hardness variation, respectively.

0.5 nN		100 kN/m
Force resolution		Sensing element stiffness

Friction Analysis

Effects of Material Imperfections on Cutting Resistance and Surface Friction

Nothing is perfect, especially in engineering materials, where 'imperfections' like grain boundaries can enhance an alloy's strength.

In situ videos and scratch data illustrate how the Cube Corner diamond tip interacts with defects and inclusions in samples, affecting chip formation and causing machining chatter.

The aluminum 5052 marine alloy’s inclusion reduces penetration depth and increases friction significantly, while the bulk metallic glass (BMG) shows lower scratch resistance, evidenced by serrated flow due to shear banding under higher loads.

0.5 nN		100 kN/m
Force resolution		Sensing element stiffness

Scratch of Coatings

Overcoming Industrial Scaling Challenges for MoS2 Solid Lubricant Coatings

Molybdenum disulfide (MoS₂) is a popular solid lubricant coating used in various industries, particularly in applications where traditional liquid lubricants may not be suitable. They are commonly used for providing dry lubrication in bearings under challenging environmental conditions, e.g., vacuum, high load, and irradiation.

However, industrial upscaling frequently results in a different coating microstructure than the laboratory prototypes presented in the literature.

Therefore, to ensure full functionality in these coating systems, the coatings must be cohesive and well-adhered to their substrate, whether that is another coating, a silicon wafer, or precision optics.