Determination of Size Distribution of Thermal Spray Powders and the Tungsten Carbide Particle Size and distribution Present in these Powders.
EMSL Project ID
2521
Abstract
Objective: The objective of this research study is to determine the size distribution of the as-received thermal spray powder as well as the size and distribution of the tungsten carbide particles in the original powder. Approach: Coatings were produced from thermal spray powders containing 3 distinct carbide sizes, ~1µm, 200-300nm, and =100nm. The questions to be answered during this proposed study are: 1. What are the sizes and distributions of the carbides in the as- received thermal spray powders? 2. What are the sizes and distributions of the particles making up the as-received thermal spray powders? We have previously assessed cross sections of selected coating and powder samples in the PSU SEM which uses a tungsten source as well as in the EMSL FESEM in a previous study. We were able to readily detect and document the presence of micron sized carbides with the SEM. However, images of the submicron carbides produced to date were not conclusive, and the nanoscale carbides are beyond the resolution limit of the SEM. Both submicron and nanosized tungsten carbide particles were readily resolved by the EMSL FESEM. Thus, our desire to complete our studies in this area by assessing this final series of specimens with the EMSL FESEM. . The powder cross-section samples have been mounted and polished to 0.05µm. We propose to study these cross sections using the EMSL FESEM. We know that this instrument has the needed resolution to yield the desired information in a documentable format. This distribution information is as critical in establishing the structure/property relationship as the carbide size A series of images from approximately 1000x to 100,000x is desired as this would create a more complete picture of the microstructure of the samples. Scope of work: 1. Four powders to be analyzed with a particle size analyzer. 2. Two mounted powder samples to be imaged to determine carbide size and distribution. The thermal spray powder sample size distribution information requested along with the powder cross-section samples to be imaged with the FESEM will allow completion of the work previously done at EMSL. In the thermal spray process it is essential that the feedstock powder be completely characterized. In this case the feedstock consists of agglomerated spherical particles (1-100µm) with tungsten carbide particles (20 -2,000nm) in a cobalt matrix. It has been determined that feedstock characteristics are the most important variable in controlling the resultant thermal spray coating. The powder size analysis will further this understanding by showing the distribution of particle sizes in the feedstock. Feedstock powders used for thermal spray need to have certain characteristics. One of the most important characteristic is a narrow powder size distribution, as only particles in a narrow size range receive the optimal time at temperature to achieve proper melting in plume. And, thus, it is critical that the powder size distribution of the feedstock be fully characterized. Furthermore, these powders contain nanoscale carbides, and, due to the small size of carbides, it is necessary to the used a FESEM to fully evaluate the distribution of carbide sizes in the powder particles.
Project Details
Project type
Exploratory Research
Start Date
2002-06-01
End Date
2004-07-15
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members