Effect of Metal 3D Printing Process Chain on Properties of TC4 Powder

Effect of Metal 3D Printing Process Chain on Properties of TC4 Powder

-- Reprinted from 3D printing technology reference

In the powder bed laser melting technology, the material from production, transportation, storage to printing and recycling process, the powder in the entire process chain has been under a variety of mechanical and atmospheric environment, the chemical composition and shape of the powder particles, as well as the characteristics of the entire powder material, may be affected by the atmosphere, temperature, humidity and external forces and other factors.
This paper discusses the potentially important influencing factors of TC4 powder in the entire process flow, and the results can be used for other powder processing and management to ensure the quality of the material throughout the service life, making the SLM process more robust and reliable.
Powder production factors
In order to evaluate the characteristics and batch stability of the powders, the same specifications and two batches of powders produced by three different processes (gas atomization EIGA, plasma atomization PA, and inductively coupled plasma atomization ICPA) of TC4 (grade 5) were studied. The particle size distribution, particle morphology and fluidity of these powders were determined respectively.
The results show that the size of the particles of the three powders is between 15-65 microns, with a Gaussian distribution, but the PA and ICPA powders show a broader particle size distribution compared to the EIGA powder. The flow time measured by the Hall flowmeter is in the range of 14.6 s-16.1s, indicating that all powders and batches have good flowability. Electron microscopy results showed that all three powders were highly spherical, although the EIGA powder particles were slightly elongated, while the ICPA powder contained a lot of satellite powder.

Morphology of powders produced by EIGA, ICPA and PA processes

In order to evaluate the printability of each batch of powder, the process was debugged on the SLM 250HL equipment, resulting in 32 different parameter sets. For each set of process prepared specimens, pore measurements and analyses were performed separately.
The test results of the density block show that all powders (different processes and batches) can obtain cubes with a density higher than 99%. It should be noted that different processes may be applicable for each powder and batch.

Different powder printing energy density and density correspondence table.

So it can be concluded
The shape and size distribution of powder particles produced by different processes are different.
Each powder and each batch can be adjusted to obtain parts with a density of 99.9% (this also means that these differences in powder lead to the inapplicability of the same process).

Powder storage and transportation factors
In order to study the effects during transportation and storage (such as temperature and humidity), commercial powder containers were stored in a manual climate box. The temperature of the climate box was kept constant at 30°C, and the relative humidity increased from 20% to 95% within 12 days. Samples were taken daily for characterization.

Temperature and humidity scene

The results show that the values of D10, D50 and D90 have not changed significantly when statistics are made according to volume. If statistics are made according to the number of particles (the percentage of the number of particles of different sizes, as shown in the figure, D90 indicates that 90% of the number of particles are smaller than x microns), obvious coarsening behavior can be found. Therefore, it can be assumed that as the humidity increases, smaller particles adhere to larger particles, causing a change in powder size, and the flow time measured by the Hall flowmeter decreases from 15.1s to 14.7 5S (I. e., particles agglomerate over time).

Particle size distribution of the powder over time (by volume and number of particles, respectively)

To investigate whether argon protection is required during powder storage, two powder containers were stored under identical conditions of 30°C and 30% relative humidity. One container has been stored intact and the protective atmosphere of the other container is destroyed by a single opening process. After a storage period of ten days, samples were prepared for mechanical testing and elemental measurements.
The tensile test results show that the ultimate tensile strength of the sample is basically the same under the protective atmosphere and without the protective atmosphere, and the ultimate strength of the powder stored in the wet environment is the highest, which is slightly increased by 5% compared with the sample printed by dry powder, while the elongation rate decreases seriously. Gas content measurements confirmed that the oxygen content of the sample was about 10% higher in a humid environment than in a dry environment, which resulted in embrittlement of the material.

Mechanical Properties of Printed Powder in Humid Environment, Argon Protection and Without Argon Protection

Hydroxide and nitrogen content of samples under different storage conditions

The main conclusions of this section
The humidity of the powder storage environment has little effect on the particle size distribution of the powder, but the humid environment will still cause fine powder agglomeration and increase the absorption of hydrogen, nitrogen and oxygen.
Argon atmosphere has no significant effect on powder and part performance.

Effect of Monolayer Continuous Scanning Area
To investigate the powder coarsening behavior during 3D printing, the researchers designed an experimental scheme that linked the area of continuous laser scanning to the total amount of spatter formation. The experiment was divided into four groups. The total volume of all printed parts was the same, but the number of parts was divided into 1, 4, 16, and 64. After each printing, the powder particle size was measured.

same volume, but different areas of continuous scanning of the monolayer

The test results show that there is no significant difference in the final powder particle size of the four printing methods, which proves that the continuous scanning area has no effect on the coarsening of the powder.

Average distribution of particle size after different consecutive scans

However, the absorption of nitrogen and oxygen can be detected in all samples, especially for the "1:1" sample absorption is very high. For the raw powder, an oxygen content of 841ppm and a nitrogen content of 178ppm were measured. The researchers believe that the larger area of continuous scanning leads to an increase in the temperature of the sample, which increases the affinity of the structure for gas absorption.

Nitrogen and oxygen absorption of samples with different continuous scanning areas

In view of the influence of powder recycling on product quality stability, the experimental scheme is designed as follows: the same batch of powder is printed 17 times continuously, during which no new powder is added. After each printing is completed, the powder is thoroughly screened. Before each manufacturing work, the powder of this experiment will be tested for particle size. The prepared samples were tested in a tensile test and the absorption of the gas content was determined. All samples were tested in the as-printed condition.
The test results show that the powder particle size D10, D50, D90 with the increase of the number of cycles have no obvious change. The digitally high deviation of the D90 value may be due to insufficient sampling.

Particle size change during powder recycling

The tests of the mechanical properties also showed no significant changes, a slight increase in the yield strength and a decrease in the elongation, and only a slight embrittlement could be considered.

Mechanical test results under different cycles

The embrittlement can be explained by the change in oxygen content with increasing number of cycles. From the beginning to the end of the test, the absorption of oxygen content increased by about 20%, which may be due to the increase in the number of cycles, the powder with higher oxygen content in the splash more and more, this phenomenon in the AlSi10Mg study also found similar results.

Absorption of nitrogen, oxygen and hydrogen at different cycles

Conclusions drawn in this section
In continuous large area scanning, the absorption of hydrogen, oxygen and nitrogen will increase. To avoid this phenomenon in industrial applications, attention should be paid to the printing direction and scanning strategy to minimize this effect.
After 17 production cycles, an increase of about 20% in the content of hydrogen, oxygen and nitrogen was detected, and the material showed a tendency to embrittlement.
The comparative study of the mechanical properties of SLM samples under different cycles found that there was no significant correlation between the mechanical properties and the number of powder cycles.

 END         
The conclusions of this study are instructive, but not sufficient to serve as a standard for powder management in this industry. There have been similar studies in China for a long time, and the results are consistent and different. Interested readers can use them for comparison as a reference.
In the actual industrial production, the preservation of powder should be kept dry, and the addition of new powder from time to time can also be used as an effective way to ensure quality. With the deepening of research, the management of powder should gradually have a clear standard.

Temperature and humidity scene

The results show that the values of D10, D50 and D90 have not changed significantly when statistics are made according to volume. If statistics are made according to the number of particles (the percentage of the number of particles of different sizes, as shown in the figure, D90 indicates that 90% of the number of particles are smaller than x microns), obvious coarsening behavior can be found. Therefore, it can be assumed that as the humidity increases, smaller particles adhere to larger particles, causing a change in powder size, and the flow time measured by the Hall flowmeter decreases from 15.1s to 14.7 5S (I. e., particles agglomerate over time).

Particle size distribution of the powder over time (by volume and number of particles, respectively)

To investigate whether argon protection is required during powder storage, two powder containers were stored under identical conditions of 30°C and 30% relative humidity. One container has been stored intact and the protective atmosphere of the other container is destroyed by a single opening process. After a storage period of ten days, samples were prepared for mechanical testing and elemental measurements.
The tensile test results show that the ultimate tensile strength of the sample is basically the same under the protective atmosphere and without the protective atmosphere, and the ultimate strength of the powder stored in the wet environment is the highest, which is slightly increased by 5% compared with the sample printed by dry powder, while the elongation rate decreases seriously. Gas content measurements confirmed that the oxygen content of the sample was about 10% higher in a humid environment than in a dry environment, which resulted in embrittlement of the material.

Mechanical Properties of Printed Powder in Humid Environment, Argon Protection and Without Argon Protection

Hydroxide and nitrogen content of samples under different storage conditions
The main conclusions of this section
The humidity of the powder storage environment has little effect on the particle size distribution of the powder, but the humid environment will still cause fine powder agglomeration and increase the absorption of hydrogen, nitrogen and oxygen.
Argon atmosphere has no significant effect on powder and part performance.

Effect of Monolayer Continuous Scanning Area
To investigate the powder coarsening behavior during 3D printing, the researchers designed an experimental scheme that linked the area of continuous laser scanning to the total amount of spatter formation. The experiment was divided into four groups. The total volume of all printed parts was the same, but the number of parts was divided into 1, 4, 16, and 64. After each printing, the powder particle size was measured.

same volume, but different areas of continuous scanning of the monolayer

The test results show that there is no significant difference in the final powder particle size of the four printing methods, which proves that the continuous scanning area has no effect on the coarsening of the powder.

Average distribution of particle size after different consecutive scans

However, the absorption of nitrogen and oxygen can be detected in all samples, especially for the "1:1" sample absorption is very high. For the raw powder, an oxygen content of 841ppm and a nitrogen content of 178ppm were measured. The researchers believe that the larger area of continuous scanning leads to an increase in the temperature of the sample, which increases the affinity of the structure for gas absorption.

Nitrogen and oxygen absorption of samples with different continuous scanning areas

In view of the influence of powder recycling on product quality stability, the experimental scheme is designed as follows: the same batch of powder is printed 17 times continuously, during which no new powder is added. After each printing is completed, the powder is thoroughly screened. Before each manufacturing work, the powder of this experiment will be tested for particle size. The prepared samples were tested in a tensile test and the absorption of the gas content was determined. All samples were tested in the as-printed condition.
The test results show that the powder particle size D10, D50, D90 with the increase of the number of cycles have no obvious change. The digitally high deviation of the D90 value may be due to insufficient sampling.

Particle size change during powder recycling

The tests of the mechanical properties also showed no significant changes, a slight increase in the yield strength and a decrease in the elongation, and only a slight embrittlement could be considered.

Mechanical test results under different cycles

The embrittlement can be explained by the change in oxygen content with increasing number of cycles. From the beginning to the end of the test, the absorption of oxygen content increased by about 20%, which may be due to the increase in the number of cycles, the powder with higher oxygen content in the splash more and more, this phenomenon in the AlSi10Mg study also found similar results.

Absorption of nitrogen, oxygen and hydrogen at different cycles

Conclusions drawn in this section
In continuous large area scanning, the absorption of hydrogen, oxygen and nitrogen will increase. To avoid this phenomenon in industrial applications, attention should be paid to the printing direction and scanning strategy to minimize this effect.
After 17 production cycles, an increase of about 20% in the content of hydrogen, oxygen and nitrogen was detected, and the material showed a tendency to embrittlement.
The comparative study of the mechanical properties of SLM samples under different cycles found that there was no significant correlation between the mechanical properties and the number of powder cycles.

END

The conclusions of this study are instructive, but not sufficient to serve as a standard for powder management in this industry. There have been similar studies in China for a long time, and the results are consistent and different. Interested readers can use them for comparison as a reference.
In the actual industrial production, the preservation of powder should be kept dry, and the addition of new powder from time to time can also be used as an effective way to ensure quality. With the deepening of research, the management of powder should gradually have a clear standard.