Elastic-plastic-brittle transitions of potassium dihydrogen phosphate crystals: characterization by nanoindentation

Abstract

Potassium dihydrogen phosphate (KDP) crystals are widely used in laser ignition facilities as optical switching and frequency conversion components. These crystals are soft, brittle, and sensitive to external conditions (e.g., humidity, temperature, and applied stress). Hence, conventional characterization methods, such as transmission electron microscopy, cannot be used to study the mechanisms of material deformation. Nevertheless, understanding the mechanism of plastic-brittle transition in KDP crystals is important to prevent the fracture damage during the machining process. This study explores the plastic deformation and brittle fracture mechanisms of KDP crystals through nanoindentation experiments and theoretical calculations. The results show that dislocation nucleation and propagation are the main mechanisms of plastic deformation in KDP crystals, and dislocation pileup leads to brittle fracture during nanoindentation. Nanoindentation experiments using various indenters indicate that the external stress fields influence the plastic deformation of KDP crystals, and plastic deformation and brittle fracture are related to the material's anisotropy. However, the effect of loading rate on the KDP crystal deformation is practically negligible. The results of this research provide important information on reducing machining-induced damage and further improving the optical performance of KDP crystal components.

Effect of Anisotropy of Potassium Dihydrogen Phosphate Crystals on Its Deformation Mechanisms Subjected to Nanoindentation

“…48 After the initial elastic stage, the first "pop-in" appears in the load−displacement curve, as shown in Figure 2, which complies with the experimental observations. 17,49 After the first "pop-in", the indentation force increases more slowly than that predicted by the JKR theory, indicating that inelastic deformation occurs. 50−52 In addition, "pop-in" events appear more frequently on the (001) surface than that on the (100) surface as shown in Figure 2, which is consistent with the experimental results.…”

Investigation of elastoplastic deformation in potassium dihydrogen phosphate crystals through nanoindentation and ultra-precision fly cutting experiments

“…These experiments yielded information regarding properties, such as hardness and elastic modulus on the doubler plane of KDP crystals, as well as the observation of size effects 14 – 17 discovered that KDP crystals may undergo complex visco-elasto-plastic deformation at the micro/nanoscale, with plastic deformation being initiated by mechanisms, such as dislocation nucleation and propagation. Obtaining mechanical parameters through nanoindentation experiments is a complex process.…”

“…The peak forces applied were set at 10, 15, 110, 130, and 170 mN. Nanoindentation experiments were performed using a Berkovich indenter with an included angle of 142.35 deg, and the project area function for the nanoindentation experiments can be found in reference, 17 given as A=25.4h2+4043.1h−69792h0.5+123430h0.5.…”

Thermodynamic Modeling the Solid–Liquid Phase Equilibrium of a Water–Methanol–Potassium Dihydrogen Phosphate Ternary System with a Mixed-Solvent Electrolyte (MSE) Model

“…Potassium dihydrogen phosphate (MKP) is an important phosphorus chemical product with high value and widespread use. It is applied in the industry, feed, agriculture, food, pharmaceutical, and other fields. , Especially in agriculture, MKP is an important fertilizer, which is an efficient chlorine-free phosphorus potassium compound fertilizer and has the advantages of high nutrient composition (including K 2 O 35%, P 2 O 5 52%), good fertilizer efficiency, good water solubility, and easy to be absorbed by plants. − In recent years, with the development of water-soluble fertilizers, the demand for MKP in agriculture increases. At present, the relatively mature production method of MKP is the neutralization method with thermal process phosphonic acid as the raw material, but the raw materials of this method are expensive; therefore, this method is not suitable for the production of MKP for practical use in agriculture. − Therefore, potassium chloride and wet phosphoric acid are used as raw materials to reduce the production cost.…”

“…Potassium dihydrogen phosphate (MKP) is an important phosphorus chemical product with high value and widespread use. It is applied in the industry, 1 feed, 2 agriculture, 3 food, 4 pharmaceutical, 5 and other fields. 6,7 Especially in agriculture, MKP is an important fertilizer, which is an efficient chlorinefree phosphorus potassium compound fertilizer and has the advantages of high nutrient composition (including K 2 O 35%, P 2 O 5 52%), good fertilizer efficiency, good water solubility, and easy to be absorbed by plants.…”