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Segment fabrication


Segment fabrication has 3 basic stages:

1. Metal powder and diamond preparation
2. Metal powder and diamond blending
3. Pressing and sintering


Mixer diamnd metal powders

U n it v o l u me o f bon d S e g m e n t

Diamond thermal stability

Mechanisms for the high-temperature strength degradation of diamond are:
Internal graphitisation
Occurs around metallic inclusions comprising solvent/catalyst metal. It can begin to occur at around 700°C where diamond starts to be re-catalysed back to graphite. Graphite is more stable at these temperatures and pressures and has a greater volume per unit mass, therefore, the diamond starts to expand internally stress.

Surface oxidation
Heat energises the breaking of carbon–carbon bonds on the diamond surface and oxygen reacts with the carbon carbon oxides. This creates pitting on the diamond surface; this reaction occurs more readily at defects (e.g. dislocations).

Surface graphitisation
Is caused by catalyst metals (Co, Fe) in the segment matrix. Diamond is converted back to graphite which darkens the diamond surface. Chemical removal of this darkened surface reveals surface etching. Reactions occur more readily at defects (e.g. dislocations).

Saw diamond at room temperature in argon

Room temperature

Effect of heating in flowing argon @ 1100°C

Effect of heating in flowing argon @ 1,100°C

Saw diamond

Room temperature

Effect of heating in static air @ 1100°C

Effect of heating in static air @ 1,100°C

Saw diamond at room temp

Room temperature

Effect of sintering in Fe bond @ 900°Cs

Effect of sintering in Fe bond @ 900°C

Graphitsation

Graphitsation

Reduced graphitsation due to the coating

Reduced graphitsation due to coating


Cutting Rate Height of Protrusion Matrix B a se p l ane T op p l a ne Height of Protrusion

Height of diamond protrusion
The theoretical height of diamond protrusion, as a function of cutting rate is shown in the diagram.

Initially, protrusion height increases rapidly, due to bond erosion, and then flattens off.
Diamond size determines an upper limit to the maximum protrusion height (if the adhesion between the diamond and the bond is sufficient). The diamond's structure and properties limit the protrusion height if wear occurs by microfracture.


How coatings work
Retention - the weak link theory:
"A chain is only as strong as its weakest link".

The role of coatings is to protect diamond during tool manufacture and enhance diamond retention in abrasive applications.
Successful implementation of coatings depends on a balanced coating-bond interaction, tool design which considers the effect of coatings on performance (higher power) and that the toolmaker employs good tool making practices.

Di a m ond - C oa t i n g Di a m ond - Di a m on d C oa t i ng - M a t r i x M a t r i x - M a t r i x

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