Ablation Abrasion

Ablators, in tumescent Ablators, melting Ablators, subliming Abortifacients Abortion, habitual AB polyamides Abrasion index Abrasion tests Abrasive... 

Figure 10.32 Abrasion-ablation model of relativistic nuclear collisions.

Spark ablation is very abrasive when performed under liquid. Barnes and Malmstadt [138] used this effect to reduce errors stemming from sample inhomogeneity in classical spark emission spectrometry. The approach is also useful for the dissolution of refractory alloys, which are highly resistant to acids [139]. When sparking under liquid, ablation rates up to ca. 3 mg/min can easily be achieved. In high-alloy Ni-Cr steels, electron probe micrographs show that selective volatilization can become problematic. Very stable colloids can be formed when a ligand such as ethylenediaminetetraacetic acid is present in the liquid. 

It could be argued that, in spite of the exeellent results seen when using corona discharge, plasma treatment and laser ablation surfaee pretreatment techniques, it is unlikely that they will be cost effective and will be difiheult to introduce for the treatment of large components. However, in view of the poor performances now often seen by using conventional abrasion techniques, it is probable that ways round these difficulties will have to be found. 

Two types of ultrasonic machining are currently used ultrasonic sink and ultrasonic path machining. In the case of sink machining the ablation rate is highest in front of the tool. At the sides of the tool the ultrasonic amplitude in normal direction to the surface is rather small, which results in a rolling of the abrasive particles so that the particles cause no direct impact in the work piece. A review of ultrasonic machining can be found in the literature [517]. 

The action of ultrasonic-activated abrasive particle suspension determines the materials removal rate, which is affected by the particles itself, their size and concentration in the suspension. The ideal abrasive particles have high hardness and high compressive strength, a lot of sharp edges and usual fracture behaviour [281,282]. The use of diamond particles allows high ablation rates because of their enormous hardness. However, they are expensive. Boron carbide is an alternative material, which allows an ablation rate of 90% as compared to diamond grains at a significant lower cost. Silicon carbide can also be used however its ablation rate is even lower than those for boron carbide. 

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