Gradient Structured Copper by Rotationally Accelerated Shot Peening

doi:10.1016/j.jmst.2016.11.006

Abstract

Abstract:

A new technology—rotationally accelerated shot peening (RASP), was developed to prepare gradient structured materials. By using centrifugal acceleration principle and large steel balls, the RASP technology can produce much higher impact energy compared to conventional shot peening. As a proof-of-concept demonstration, the RASP was utilized to refine the surface layer in pure copper (Cu) with an average grain size of ~85 nm. The grain size increases largely from surface downwards the bulk, forming an 800 μm thick gradient-structured surface layer and consequently a micro-hardness gradient. The difference between the RASP technology and other established techniques in preparing gradient structured materials is discussed. The RASP technology exhibits a promoting future for large-scale manufacturing of gradient materials.

Key words: Microstructure, Rotationally accelerated shot peening, Gradient structure, Hardness, Copper

Wang X., Li Y.S., Zhang Q., Zhao Y.H., Zhu Y.T.. Gradient Structured Copper by Rotationally Accelerated Shot Peening[J]. J. Mater. Sci. Technol., 2017, 33(7): 758-761.

Figures/Tables 7

Fig. 1. Schematic illustration of the RASP process.

Fig. 2. Optical micrograph of the cross section of a RASP-processed Cu sample.

Fig. 3. Hardness gradient as a function of the depth of a RASP-processed Cu sample.

Fig. 4. EBSD mapping graph along the depth of a RASP-processed Cu sample.

Fig. 5. Representative TEM images of nanometer-sized grains in the top surface layer: (a) Bright field image and SAED pattern (inset); (b) dark field image; (c) histograms of transverse grain sizes (dt) and (d) longitudinal grain sizes (dl). The inset in (d) is the aspect ratio (dt/dl) distribution.

Fig. 6. Microstructure at different depths from surface: (a) ~50 μm, (b) ~130 μm, (c) ~200 μm, and (d) ~300 μm.

Table 1 Comparison of process parameters between RASP and other techniques

Technique	Diameter of balls or shots (mm)	Impact velocity (m s^-1)	Density of balls (g cm^-3)	Kinetic energy of balls (J)
Shot Peening^[19]	0.25-1	20-150	7.74	3.2 × 10^-5-0.12
USP^[20,21]	3-7.5	<20	7.98	0.06-0.9
SMAT^[22,23]	3-8	2-5	7.98	6 × 10^-4-0.07
SNH^[24]	5-7.9	~5	14.5	0.03-0.12
RASP	1-8	5-80	7.8	1.3 × 10^-4-17

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