DOI: 10.5281/zenodo.18714678
title: Spherical scratch data

description: The attached ZIP file contains experimental test data from variable temperature spherical tip scratch and indentation on high-purity, cold-worked pure tungsten (W). It includes individual folders by test number, where file names explain the conditions, including temperature and, for scratches, sliding speed. This is the supplementary data supporting the manuscript titled, "Uniaxial Tensile Mechanical Properties from a Scratch on Ultrafine Grained Tungsten", current (in 2026) in peer review at Proceedings of the Royal Society A. Further experimental details are available via the publication. The contents of the methods section of the manuscript are provided as a separate description attached to this file. 
description: Material Preparation

The tungsten targets (99.98% purity, 1” diameter x 0.250” thickness) where purchased from ESPI Metals (Espicorp, Inc.). Samples were then wet polished using SiC with progressively finer grits of 800,1000, and 1200. A final set of polishing passes were performed using 6, 3, and 1 µm diamond suspensions, then 0.05 µm colloidal silica, each for 3 hours, using a 5 min ultrasonic water bath in between each step. The polished surfaces exhibit root-mean-square (RMS) and average roughness of 500-550 nm and 400-500 nm, respectively, with a typical skewness between 0 and 0.5, as measured using a white light interferometer.

Spherical Scratch and Indentation Testing

Scratch and indentation testing were performed using an Rtec MFT-5000 Multi-Function Tribometer equipped with an integrated scanning white-light interferometer (SWLI) profilometer. A spheroconical diamond tip with a 200 µm tip radius and 60° cone half-angle was used for all tests. Scratches and indents were produced on polycrystalline tungsten substrates under both ramped and constant normal load conditions.

Ramped-force scratch tests applied a continuously increasing normal force from 0 to 100 N over a 25 mm scratch length. This range was selected to allow accurate measurements of depth-dependent track dimensions and enabling sampling of a larger total volume of material. All scratches were performed at a lateral tip translation speed of 0.01 mm/s. A correction for tip deflection was applied to all force measurements to accurately correlate forces with surface locations, since the tip deflection is significant and introduces an error between the commanded stage position and true contact location on the surface. All tests were performed in ambient lab air, at approximately 20°C and 20% relative humidity, unless otherwise stated for high-temperature tests.

Bi-axial force data, normal and lateral, were recorded during each scratch with a frequency of 1 kHz. Post-scratch surface profiles were obtained using the SWLI, from which scratch penetration depth was directly measured.

Microscopy and Microstructural Analysis

An FEI Teneo field-emission SEM with Oxford Instruments energy-dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD) detectors was used for the microstructural analysis of the tungsten target specimen, the working distance was 8 mm and the accelerating voltage was 20 kV, with a 0.2 nA current for EBSD. The step size of the EBSD analysis was 0.04 µm.

Grain size distributions were determined from EBSD orientation maps using the equivalent circular diameter (ECD) method, excluding grains with a confidence index below 0.1. The average grain diameter was 650 ± 80 nm. EBSD and EDS phase maps revealed that >99% of the scanned area corresponded to the BCC tungsten phase, with the remainder attributed to carbon on the surface.