in Vol. 18 - May Issue - Year 2017
Study On The Process Of Abrasion Failure Of Titanium Cut Wire Shot For Blast Cleaning
Table1: Characteristics of titanium cut wire shot
Appearance changes in difference ERVIN cycles of titanium cut wire shot (a) original appearance (b) 200cycles (c) 3000cycles (d) 6000cycles (e) 7000 cycles (f) 9000 cycles
Relationship between residual and ERVIN cycles of titanium cut wire shot
Changes of the appearance of the titanium strip after being blasted by different cycles by titanium cut wire shot
Abstract: In this composition, the hardness of 0.6mm titanium cut wire shot was measured by micro-hardness tester and the abrasion process was measured by Ervin Test Machine. A titanium alloy strip was blasted by this kind of abrasive. The results show that the hardness of titanium cut wire shot is 374.8HV; the Ervin cycle life is 5199 times; there are four stages in the whole abrasion process: rounding and passivation stage, stable wearing stage, accelerated wearing stage and severe wearing stage; the blasted titanium alloy strip has a 100% coverage rate and cleanliness which was evaluated to Sa3 Clean Level. Key words: Titanium cut wire shot; Abrasion; Ervin cycle life; Blast cleaning
Titanium alloy with high specific strength, good corrosion resistance and excellent mechanical properties, and many other advantages, is widely used in the aerospace, shipbuilding, chemical and weapons industry and other fields . Refering to a great deal of literature, there are few documents about abrasives consisting of titanium and its alloys, let alone their applications to shot and blast cleaning titanium alloy strips. In this experiment, samples were a new kind of abrasive developed by Shandong Kaitai Group Corporation, namely, 0.6mm titanium cut wire shot. The hardness was measured by micro-hardness tester and the abrasion process was measured by Ervin Test Machine . A titanium alloy strip was blasted by this kind of abrasive.
1. Samples and Experimental Procedures
1.1 Experimental material sample
These samples are made of TC4 titanium alloy wire and their particle size is 0.6 mm. Chemical components (quality percents): iron (Fe) ≤ 0.30, carbon (c) ≤ 0.10, nitrogen (n) ≤ 0.05, hydrogen (h) ≤ 0.015, oxygen (O) ≤ 0.20, aluminum (Al) 5.5~6.8, vanadium (v) 3.5~4.5, allowance for Ti, and the physical properties are all shown in Table 1.
1.2 Experimental method
Abrasion process test of titanium cut wire shot: 50 grams of these samples were weighted. Then they were put into Ervin Test Machine. Every 500 ERVIN cycles, these samples were taken out and screened through a sieve with 0.3mm aperture mesh. The next step was to weigh these remaining samples and record the remaining quality. Meanwhile, samples’ appearances were observed by using Epson V19 scanner. Next, remaining samples were put into Ervin Test Machine again until next 500 ERVIN cycles. The prior steps were repeated until samples’ quality was less than 2.5g, and then the test was stopped. According to standard SAE J445-2005 Metallic Shot and Grit Mechanical testing , the area-method  was used to calculate the Ervin life of sample.
Method detailed: shot and blast cleaning test of titanium cut wire shot: a titanium alloy strip was fixed to Ervin Test Machine. Dimension of the titanium alloy strip is: 76mm × 17mm × 4mm (length × width × thickness). Hardness of this titanium alloy strip is 223HV. Place 5g titanium cut wire shot (after 200 ERVIN cycles impact) into the Ervin Test Machine. Every a certain number of cycles, stop the machine and scan the strip, and compare it with the standard coverage test piece, until the coverage rate reach to 100%.
2. Results and Analysis
2.1 Process of Abrasion
In the whole abrasion failure process of titanium cut wire shot, 0~ 200 ERVIN cycles were the rounding and passivation stage. Titanium cut wire shot gradually became spherical during the impact process; 200~6000 ERVIN cycles were the stable wearing stage. At this stage, plastic deformations continuously occurred because titanium cut wire shot absorbed part of the kinetic energy  occurring in the superficial layer work hardening. More and more distortions and sharp corners appeared on the face of the titanium cut wire shot due to the shear stress. After repeated impacts, these protrusions became curved and separated. The main weight loss was from surface breakaway . With the continual impact, particle size became smaller and smaller. Some samples were just screened off by the mesh; 6000~7000 ERVIN cycles were the accelerated wearing stage. Micro cracks extended to the surface, the surface breakaway accelerated and mass lost increased; 7000~9000 ERVIN cycles induced severe wearing stage where massive shedding phenomena always occurred.
2.2 Ervin life Test by Area-method
The area surrounded by the curve was calculated, and then divided by the samples’ original mass (50g). As a result, ERVIN cycles life of titanium cut wire shot was 5199 times.
2.3 Appearance Changes of the Blasted Strip
Just after being blasted for 60 cycles by titanium cut wire shot, the titanium strip had a 100% coverage rate. The surface became pure and clean, and the roughness was around 2.9μm (Ra).
Titanium cut wire shot has a compacted and homogeneous structure, and its abrasion process is very stable. There are barely fissure and break phenomena in its long practical life. The workpieces have very bright and clean surfaces after being blast-cleaned by titanium cut wire shot. Since titanium cut wire shot does not have any magnetism at all, it can be used in a magnetic environment or other specific environments. The results show that the hardness of titanium cut wire shot is 374.8HV; the Ervin cycle life is 5199 times; there are four stages in the whole abrasion process: rounding and passivation stage, stable wearing stage, accelerated wearing stage and severe wearing stage; the blasted titanium alloy strip has a 100% coverage rate and cleanliness, which was evaluated to Sa3 Clean Level.
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Wenlong Zhu, Ruwei Liu, Hongcong Sun
College of Materials Science and Engineering
Shandong University, Jinan 250061, P.R.China,
Shouquan Zhang, Jian Wang, Ga Zhang
Shandong Kaitai Group Co.,LTD
Zouping Binzhou 256217, P.R.China
Corresponding author: Ruwei Liu