® ceramics are now used with increasing frequency in pump & valve applications. This increase in use is firmly rooted in the excellent erosive wear resistance of Technox® zirconia. This data sheet attempts to explain the mechanics of erosive wear behaviour and provide independent, third party, data about the comparative performance of Technox® vs other materials.
The Erosive Wear Process

The process of erosive wear occurs by the impact of particles upon a surface with a resultant loss of material due to fracture, spalling and/or abrasive wear of the impacted surface.
Erosive Wear Behaviour of Metals vs. Ceramics

Erosive wear can occur in both metals and ceramics. However, due to their high hardness, ceramics are generally more resistant to erosive wear. Yet there are significant differences between the two classes of material: with a metal (which displays ductile deformation behaviour) the impact of abrasive particles at 90° to the horizontal is less damaging than more acute impact angles, but with ceramics, where the deformation mode tends towards brittle fracture, 90° impacts cause the most damage.
Hardness vs. Toughness

Recent experimental evidence for ceramic materials has shown that although hardness is an important parameter in controlling erosive wear, of greater importance is the ratio of hardness/toughness. In simple terms one can interpret these results as follows:

· A hard but brittle ceramic will resist indentation by a hard indenter, but the surrounding “brittle” surface may crack, leading to the removal of a significant amount of material, and hence significant wear.

· A softer but tougher ceramic may display higher indentation damage, but the toughness of the material will avoid any surface cracking and hence the removal of large amounts of surface material, thus reducing wear.

These theories have now been tested by experiment as detailed below. The aim of this work was to monitor the performance of several candidate materials for pumping applications.
Erosive Wear Test Data

Rods of the candidate materials and coatings (10 mm diameter, 30 mm long) were placed in the outlet stream of a high pressure water jet under the conditions indicated. The volume loss of each material was measured as a relative % of the volume loss from a stainless steel 316 control pin, i.e. the lower the value the more wear resistant the material. The obvious conclusion to be drawn from these results is that Technox 2000® displays excellent wear performance under conditions of both erosive and erosive/corrosive wear. The wear performance of the zirconia being some 5-18 times better than that of the Tungsten Carbide 6% Cobalt materials.

AZoM- Metals, ceramics, polymers and compsites - Wear test data for various pump candidate materials includinh Technox 2000 zirconia ceramic from Dynamic-Ceramic.

Figure 1. Wear test data for various pump candidate materials.




Test 1


Test 2

Jet velocity (m/s)


25


25

Sand content (ppm)


1000


1000

Test duration (mins)


30


30

Impact angle (degrees)


45


90

pH


7


5.5
Cavitation

In addition to the excellent erosive wear resistance Technox® ceramics also display excellent cavitation resistance. The uniform and homogeneous microstructure, coupled with high densities and corrosion resistance promote low material loss during turbulent flow conditions. A factor which affects cavitation resistance is the quality of surface finish. High degrees of polish lengthen the period before cavitation erosion begins.

AZoM- Metals, ceramics, polymers and compsites - Cavitation test data generated by University of Coventry. Test conditions were 20kHz and 50µm of displacement.

Figure 2. Cavitation test data generated by University of Coventry. Test conditions were 20kHz and 50µm of displacement.
Typical Applications

Technox® ceramics have a well established pedigree in many oil-field and downhole installations throughout the world. Typical applications include:

· Plug stems and valve seats

· Choke trims

· Choke beans

· Movable orifice valves

· Gate valve seats

· Ball valves and seats

· Mud pump nozzles

· Turbo drill components.