[1]Evaluation index of metal powder for additive manufacturing (3D printing) _ Metal 3D printing powder

       As a new generation of advanced manufacturing technology, additive manufacturing (3D printing) has developed rapidly in recent years. However, for the industrial metal 3D printing field, powder consumables are still one of the important factors restricting the large-scale application of this technology. At present, domestic industry standards or national standards such as metal 3D printing material standards, process specifications, and parts performance standards have not yet been formulated. The evaluation indicators for metal powder in the industry mainly include chemical composition, particle size distribution, powder sphericity, fluidity, and bulk density. Among them, chemical composition and particle size distribution are commonly used indicators for evaluating the quality of metal powder in the field of metal 3D printing, and sphericity, fluidity, and loose density can be used as reference indicators for evaluating quality.

 

1. Chemical composition

The actual mass percentage (wt.%) of each element in the metal powder.

 

Table 1 316L stainless steel composition

The above table is an example. The detection data of Ni in the alloy is 13.02, which means that the mass percentage of Ni in the alloy is 13.02%, and the mass percentages of other elements can be deduced by analogy. At present, the most widely used methods for detecting the chemical composition of metals are chemical analysis and spectral analysis. The chemical analysis method uses chemical reactions to determine the composition of metals, which can achieve qualitative and quantitative analysis of the chemical composition of metals. Spectroscopic analysis is to determine the chemical composition and approximate content of the metal by using the unique characteristic spectra generated by various elements in the metal under high temperature and high energy excitation. It is generally used for qualitative analysis of the chemical composition of metals. The above two methods must use professional testing equipment and be completed by professional personnel from professional testing institutions.

The chemical composition of most as-cast and forged metals has corresponding industry standards or national standards to evaluate whether the chemical composition indicators of the metal are qualified. However, the powder technology used for metal 3D printing is novel, and there is no corresponding industry standard or national standard in the industry. The generally recognized evaluation method in the industry is to follow the as-cast standard corresponding to the metal powder, or to relax the indicators based on the standard. Claim.

For metal 3D printing, the elements exist in liquid form after the metal is remelted during the printing process, or there may be volatilization loss of volatile elements, and the powder form has problems such as satellite spheres and hollow powder, so it may be locally Generate pore defects, or cause the composition of the printed parts to be different from the composition of the original powder or master alloy, thereby affecting the compactness of the workpiece and its mechanical properties. Therefore, for metal powders of different systems, the oxygen content is an important indicator. Taking titanium alloy as an example, the industry’s general requirement for this indicator is 1300~1500ppm, that is, the mass percentage of oxygen in the metal is 0.13 ~0.15%. Since the current powder preparation technology used for metal 3D printing is mainly atomization (including supersonic vacuum gas atomization and rotating electrode atomization technologies), the powder has a large specific surface area and is prone to oxidation. Therefore, the atmosphere must be strictly controlled during the powder preparation process. In special applications such as aerospace, customers have stricter requirements on this indicator. Some customers also require the control of the nitrogen content index, which is generally required to be below 500ppm, that is, the mass percentage of nitrogen in the metal is below 0.05%.

To be continued...