# Aging Structure, Mechanical Properties, and ZnO Piezoelectric Coating-Based Ultrasonic Response of 15CrMo Steel

## TL;DR

This paper studies how aging affects the structure and properties of 15CrMo steel with ZnO coatings used for ultrasonic testing.

## Contribution

A novel ZnO piezoelectric coating method is introduced to improve ultrasonic signal coupling on 15CrMo steel surfaces.

## Key findings

- Aging causes pearlite spheroidization and carbide coarsening in 15CrMo steel.
- Hardness and strength decrease significantly with increased aging.
- Ultrasonic wave velocity increases with higher spheroidization grades.

## Abstract

The ZnO piezoelectric coatings were deposited on the surface of 15CrMo steels by magnetron sputtering to directly excite the ultrasonic signal, effectively solving the coupling problem between the traditional probe and the pipe surface. The microstructure, mechanical properties, and ultrasonic longitudinal wave velocity of the aged samples were carried out systematically. The spheroidization grade of pearlite, evolution of carbide morphology, hardness, strength, and ultrasonic wave velocity were systematically analyzed. As the degree of aging intensifies, the material undergoes significant pearlite spheroidization and carbide coarsening. The Vickers hardness drops from 158 HV in the original state to 134.2 HV, and the yield strength and tensile strength decrease by 22.7% and 17.9%, respectively. The ultrasonic longitudinal wave velocity shows a monotonically upward trend with the increase in spheroidization grade, increasing from 5925.6 m/s in the original state to 5976 m/s at the highest spheroidization grade.