NEWS
Subject: Wear Testing of Sintered B4C and Al2O3 Sheet Stock
Author: Fred Miller
Date: l7Jun02
Preface:
World Magnetics has been approached to be a substitute vendor for the 30 channel MICR read head used in the IBM 3890. Their materials of choice for head wear surfaces are Boron Carbide and Aluminum Oxide.
Purpose:
The purpose of this evaluation is to compare the wear durability of Boron Carbide (B4C) and Aluminum Oxide (Al2O3) with the values for plasma sprayed Chromium Carbide and Aluminum Oxide / Titanium Dioxide ceramic as presented in a previous wear test report dated 07JUNOl.
Boron Carbide sheet is considerably different from the plasma sprayed Chromium Carbide in surface finish and texture. The B4C sheet is a sintered material that has the consistency and surface finish of tempered glass. Plasma spraying of the Chromium Carbide produces a material with a grainy consistency that needs to be machined to produce a smooth bearing surface.
The Aluminum Oxide sheet and the plasma sprayed Aluminum Oxide / Titanium Dioxide are similar materials. Both are ceramics. The primary difference is in the processing and application of the material. The Aluminum Oxide sheet is a ceramic produced under pressure similar to a sintered material. The resultant material is dull in appearance but similar to glass plate in texture. As with the plasma sprayed Chromium Carbide, the plasma sprayed Aluminum Oxide/ Titanium Dioxide ceramic is grainy and pitted and requires machining.
Both of these materials were provided to IBM by World Magnetics in solid sheet or block form. When used as a wear surface on a head the sheets are bonded to the head surface and ground to the proper shape. One clear advantage of these materials over the plasma sprayed materials is the elimination of high temperatures during the application process. A high level of care must be taken when applying plasma sprayed materials not to put too much heat into the assembled head or coil damage may result.
Equipment:
Taber Abrader Model 601; Mettler Electronic Balance Model AB304-S; Boron Carbide sheet provided by Ceradyne, Inc.; Aluminum Oxide sheet provided by Coors Porcelain Company
Procedure:
This test was performed according to ASTM Standards C50l-84 Vol. 15.02 Glass and Ceramics and D 4060-95 Vol. 06.01 for Paints.
Results:
The original wear test on the plasma sprayed materials involved a duration of 1000 cycles. The testing of Boron Carbide started with 1000 Cycles but the resultant weight loss was so small that the duration was increased to 5000 cycles.
All tests were performed using a 1000 gram load for 5000 cycles.
Results: Test #1 Wheel CS-17 5000 cycles |
||
Boron Carbide |
initial sample weight |
99.2340 gr |
weight loss @1000 cycles |
0.0000 gr |
|
Total Weight Loss |
and weight loss @5000 cycles |
0.0006 gr |
Results: Test #2 Wheel CS-17 5000 cycles |
||
Aluminum Oxide |
initial sample weight |
37.3791 gr |
weight loss @500 cycles |
0.0035 gr |
|
weight loss @1000 cycles |
0.0056 gr |
|
weight loss @2000 cycles |
0.0064 gr |
|
weight loss @3000 cycles |
0.0081 gr |
|
weight loss @4000 cycles |
0.0088 gr |
|
Total Weight Loss |
and weight loss @5000 cycles |
0.0092 gr |
Chromium Carbide Plasma: The average weight loss for the Chromium Carbide plasma sprayed coating over 1000 cycles with a CS-17 wheel was 0.0256 gr.
Titanium Oxide Ceramic Plasma: The average weight loss for the Titanium Oxide Ceramic plasma sprayed coating over 1000 cycles with a CS-17 wheel was 0.0328 gr.
On a volume basis the amount of loss in each case is:
IBM Test Material / Wear Performance
Chromium Carbide 0.16 cc/gr X .0256 gr = .0041 cc
Titanium Dioxide Ceramic 0.286 cc/gr X .0328 gr = .00938 cc
World Magnetics Wear Performance
Boron Carbide 0.403 cc/gr X .0006 gr = .00024 cc
Aluminum Oxide 0.266 cc/gr X .0092 gr = .0024 cc
Conclusions: The above tests indicate that on a per weight basis the Boron Carbide sheet is 16X more durable than the Aluminum Oxide sheet. Both the Boron Carbide and the aluminum Oxide are many times more durable than either of the plasma sprayed alternatives in spite of the fact that the earlier tests were run for only 1000 cycles.
On a volume basis the Boron Carbide is still 10X more durable than the Aluminum Oxide. Again, both the Boron Carbide and the Aluminum Oxide are more durable than the flame sprayed materials by wide margins. Volume wear is the parameter that indicates if the head has reached its useful life.
The wear resistance of the Boron Carbide sheet is surprising considering the fact that the CS-17 abrasive wheels that were used in the test are some of the harshest available.
By comparing the plasma sprayed Aluminum Oxide/Titanium Dioxide and the Aluminum Oxide sheet, which are similar in material makeup, it is apparent that the sintering process used in the manufacture of the sheet has a large effect on the wear resistance of the material.
This test seems to make clear that plasma spraying wearing coatings, with its inherent application problems, is not the best way to apply a wear surface to a magnetic head. Sheet or block material is more easily applied which results in fewer manufacturing process yield problems.
