Environmental Factors Affecting Wear Resistance Of Refractory Materials

Based on a comprehensive analysis of both the service characteristics of materials and environmental factors, domestic researchers in the field of refractories have continuously simulated the material erosion process and explored the mechanisms of wear and damage. The wear resistance of refractory materials is a parameter influenced by multiple factors, primarily including the following three aspects: environmental factors (such as abrasive erosion angle, abrasive erosion speed and concentration, erosion time, ambient temperature, etc.); abrasive properties (such as abrasive hardness, shape, particle size, density, crushability, etc.); and target material properties (such as composition, structure, hardness, and physical and mechanical properties). Below is a discussion of the influence of environmental factors on the erosion of refractory materials:

01. Erosion Angle

The angle formed between the incident velocity of abrasive particles and the eroded surface is referred to as the erosion angle, sometimes also called the attack angle. The influence of the erosion angle on the erosion rate of the target material remains largely unaffected by variations in abrasive particle size, type, or even velocity. However, when comparing different target materials, the impact of the erosion angle on the erosion wear rate can vary significantly.

For typical ductile materials (such as most metals and alloys), the erosion wear rate increases with the abrasive erosion angle. When the erosion angle reaches approximately 20°, the wear reaches its maximum value. After a short period of steady-state erosion, the wear rate gradually decreases. In contrast, for typical brittle materials (such as glass, ceramics, and refractory bricks), the erosion rate increases with the abrasive erosion angle, and the maximum erosion rate occurs when the erosion angle is 90°.

The relationship between the attack angle and the erosion rate for these two typical erosion failure modes can be expressed by Equation (1):

In Equation (1), ε denotes the erosion rate, α represents the erosion angle, and n, A, and B are constants. For typical brittle materials, A=0; for ductile materials, B=0, and n=π/(2α). The influence of various erosion angles on the erosion-wear resistance of QAl9-4 aluminum bronze rods was investigated. The results indicate that within the erosion angle range of 0° to 30°, the cumulative mass loss of the aluminum bronze specimens increases as the erosion angle increases; however, when the erosion angle exceeds 30°, the cumulative mass loss begins to decrease. As the erosion angle increases, the surface defects on the specimens caused by erosion wear evolve from long furrows along the direction of water flow to short furrows with pits, and the average surface roughness of the specimens decreases gradually.

02. Erosion Velocity

The velocity at which abrasive particles impact the target material is known as the erosion velocity. The influence of abrasive erosion velocity on the erosion rate is significant and can be analyzed from an energy perspective: the kinetic energy of abrasive particles upon impacting the target material serves as the energy source for the material's damage. For particles with a fixed mass and shape, the higher the velocity, the greater the initial impact kinetic energy. Therefore, erosion velocity plays a crucial role in erosion wear.

Numerous experiments have shown that there is a critical value for the erosion velocity of abrasive particles. In other words, the target material will only be damaged if the erosion velocity exceeds this critical value. This threshold is influenced by the size and shape of the abrasive particles, as well as the properties of the target material, and it can also be predicted based on the material's mechanical properties. For example, the threshold velocity for 11%Cr steel impacted by 225μm quartz sand is approximately 2.7 m/s. When the abrasive erosion velocity exceeds this threshold, the relationship in expression (2) has been summarized through erosion wear experiments conducted under different abrasives, target materials, and erosion environments:

Where v is the abrasive incident velocity, and n and K are constants. Finnie initially proposed that n≈2, which aligns with his theoretical analysis of the micro-cutting mechanism. However, subsequent experiments showed that the value of n varies from 2 to 6.5 when transitioning from ductile materials to brittle materials, with a typical range of 2 to 3. For ductile materials, the n value remains relatively stable, ranging from 2.3 to 2.4, while for brittle materials, the n value fluctuates more significantly, spanning from 2.2 to 6.5. Numerous experiments have also confirmed that the n value increases with the erosion angle.

03. Erosion Time

The period from when abrasive particles impact the target material until the end of erosion is referred to as erosion time. Unlike adhesive wear and abrasive wear, erosion wear typically has a relatively long incubation period, which is especially pronounced in liquid erosion and cavitation erosion. When abrasive particles initially impact the target, erosion wear generally does not occur immediately. Instead, the target material undergoes work hardening and becomes rough due to the impact. After some time, microcracks initiate at pre-existing defects on the target surface and propagate under continuous abrasive impact.

In sandblasting-type erosion, a "weight gain" phenomenon may occur in the early stages, caused by the embedding of abrasive particles. The magnitude of this embedding-induced weight gain is related to the erosion angle: at small incident angles, the "weight gain" phenomenon is less noticeable than at larger incident angles. It is important to note that the duration of the incubation period is a key criterion for characterizing the wear resistance of materials, as it reflects the transition from elastic deformation to plastic failure. The subsequent steady-state erosion stage is a crucial indicator for evaluating the erosion resistance of materials.

04. Erosion Temperature

Many components operate in high-temperature environments, so studying the influence of erosion temperature on materials' erosion resistance is crucial. The erosion temperature we commonly refer to can be divided into two types: first, the local temperature rise caused by friction when abrasive particles impact the target surface, which affects the target's erosion wear performance; and second, the ambient temperature of the environment where erosion occurs.

The effect of ambient temperature on phase morphology and microstructure is highly complex, making it difficult to quantitatively express the influence of temperature changes on the target's erosion wear resistance through a universal formula. Therefore, we can discuss the impact of ambient temperature on erosion wear performance based on the material properties of the target, dividing it into different scenarios:

For non-oxide materials, the wear volume-temperature curve is nearly horizontal, meaning the wear volume remains almost unchanged across the entire test temperature range.

For oxide refractory products, the trend of wear resistance with temperature can be divided into an elastic stage and a plastic stage:

In the elastic stage, the wear volume shows little to no change as the temperature increases.

When the temperature rises further and the material enters the plastic deformation stage, the wear volume decreases significantly.

Different refractory materials undergo plastic deformation at different temperatures, so the temperature at which their wear volume starts to decrease sharply varies: for high-alumina bricks, corundum bricks, and clay-bonded silicon carbide bricks, the critical temperatures are 800°C, 1000°C, and 600°C, respectively.

Erosion wear tests were conducted on SiC-Sialon composite refractories using 36# SiC as abrasive particles in an air atmosphere. The results showed that:

As the erosion temperature increased, the volume erosion rate of SiC-Sialon composite refractories initially increased and then decreased.

As the erosion angle increased, the volume erosion rate of SiC-Sialon composite refractories gradually increased.

When the ambient temperature exceeded 1000°C, oxidation occurred on the material surface, and the dense oxide protective layer formed played a key role in enhancing the material's resistance to high-temperature erosion wear.