1. Technique for the Measurement of Mechanical Strength and Fracture Characteristics of Micron Diamond
Engis R&D

2. Outline Introduction Experimental Procedures Results and Discussion
Technique Description
Experimental Procedures
Particle Size Distribution
Optical Microscopy Shape Analysis
Mechanical Crushing Analysis
Crushing Strength Index (CSI)
Crushing Characteristics
Particle Size Distribution of Crushed Diamond
Fine Particle Analysis
Results and Discussion
Comparison of Diamond Types – MB vs. RB
Comparison of Metal Bond Diamond Sources
Batch to Batch Variation in Metal Bond Diamond Powders
Conclusions

3. Introduction of New Technique
Industry standard method to measure diamond strength or friability involves impacting powder with a high density steel ball
Crushing generated mainly by impact force
Generally only applicable to mesh size diamond
In-house developed technique uses shear force to crush micron sized diamond powder
Wet crushing of diamond in glycol lubricant under controlled conditions more closely approximates lapping conditions

4. Introduction of New Technique (cont.)
Objective
To study the crushing strength and fracture characteristics of diamond powders
Application
The ability to measure the crushing strength and fracture characteristics of the diamond powders enables the user to choose an optimal diamond for the workpiece material or application
The mechanical properties of the diamond powder can be related to the performance of the final products
Tool life
Surface roughness
Material removal

5. Experimental Procedures

6. Particle Size Distribution Measurement
Particle size distribution (PSD) before and after crushing is measured by electrozone sensing method
Beckman Coulter Multisizer III
Measure number concentration of particles per gram of added powder
Known electrolyte and analytic volume
Known mass of added powder

7. Optical Microscopy Shape Analysis
Definitions:
Feret
Measured distance between parallel lines tangent to the particle boundary
ESD – Equivalent Spherical Diameter
Average of 8 feret measurements
AR – Aspect Ratio
Ratio of the shortest and longest measured feret
Feret

8. Optical Microscopy Shape Analysis Aspect Ratio Example Pictures
ELONGATED PARTICLES
Note: Pictures are in no specific order in each bin range

9. Equipment for Measuring Crushing Strength

10. Crushing Strength Apparatus
US Patent #7,275,446 B2

11. Mechanical crushing analysis
Measured amount of diamond powder dispersed 1:1 weight ratio in glycol based lubricant applied to crushing surface
Cup is raised into piston and force applied
Tools rotated in opposite directions to apply shear force
Crushed diamond collected from surface of tools
Particle size distribution measured before and after crushing on Beckman Coulter Multisizer III
Crushing strength results were averaged from three trials on each sample

12. Crushing Strength Index (CSI)
Definitions:
OSS: Number of on-size particles in the starting powder
(50-95% of distribution before crushing)
OSR: Number of on-size particles in the resulting powder
(50-95% of distribution after crushing)
CSI: Crushing strength index
CSI = OSR/OSS x 100
Number per gram
Particle Diameter

13. CSI (Example Calculation)
50% →
← 95%
Particle Diameter (mm)
Number (per gram)
50.05*106 particles (OSS)
26.88*106 particles (OSR)
= 53.7%
X 100
Number per gram calculated from known concentration of diamond in measured amount of electrolyte solution

14. Fine Particle Analysis
Crushed diamond dispersed in water by ultrasonic probe
0.1mL injected into CPS DC24000 Disc Centrifuge containing a density gradient of water and sucrose solutions
Particle size measured from 0.01mm to 4 mm
Large particles sediment immediately at high RPM speeds, and are not detected.

15. Results and Discussion

16. Particle Characterization: MB vs. RB
Particle Size
Particle Shape

17. Crushing Strength of MB vs. RB Powders
As expected, MB powders posses higher crushing strength than similarly sized RB powders.

18. Fine Particle Analysis – MB vs. RB
22-36 MB RB
15-25 MB RB
The fine particle analysis shows that the RB and MB powders exhibit different microfracturing characteristics
RB diamond generates more fine particles from crushing compared to the MB diamond.
In smaller sizes the difference in microfracturing between RB and MB diamond is less, which may be due to similar concentration of internal defects.
6-12 MB RB

19. Particle Characterization: Different MB Sources
Particle Size
Particle Shape

20. Crushing Strength of MB Powders
Diamond powders from different MB sources display significant differences between crushing strength within the same size range.

21. Fine Particle Analysis – MB Sources
22-36
MB - A
MB - B
MB - C
15-25
MB - A
MB - B
MB - C
The fine particle analysis shows that MB powders from different sources exhibit significant differences in fracture characteristics.
In smaller sizes the difference in microfracturing between MB diamond from different sources is less, which may be due to similar concentration of internal defects.
6-12
MB - A
MB - B
MB - C

22. Particle Characterization: MB Batch Variation
Particle Size
Particle Shape

23. MB Batch to Batch Comparison
Aspect Ratio alone does not correlate to crushing strength because the concentration of internal defects is related to the particular feed that was processed to produce the micron diamond powder.

24. Results & Conclusions

25. Conclusions
This technique can be used to reliably measure crushing strength and fracture characteristics of micron sized diamond powders under compressive/shear forces using a technique that simulates the lapping proces
By applying this technique we are able to quantify the variation in crushing strength and fracture characteristics in each of the following studies
Metal Bond vs. Resin Bond diamond powders
Metal Bond powders from different sources
Different batches of Metal Bond powders from the same source

26. Conclusions (cont.)
Metal Bond powders exhibit higher crushing strength and undergo less microfracturing than similarly sized Resin Bond powders
Metal Bond diamond powders from different sources exhibit significantly different crushing strength results and fracture characteristics
Different batches of Metal Bond diamond from the same source also exhibit different crushing strengths and different fracture characteristics
This may be due to the amount of internal defects which is related to the batch feed source and processing
Size and shape alone can not predict crushing strength results.

27. Thank You!
INTERTECH 2008
Orlando, Florida