Chapter 1033 The power of computational materials science
Just when everyone at Rolls-Royce was thinking about how to reversely deduce the technology used by China based on trial production samples.
At Haofa Group, the characterization analysis of the crack morphology and formation causes of titanium-aluminum alloy cubic specimens has also produced results...
"Mr. Chang, this is from 20% XRD patterns and EBSD phase diagrams of samples with different degrees of completion to 90%.”
Hang Zhibin rushed into Chang Haonan’s office and stuffed several pages of test reports that were still steaming on the paper. in the latter's hands.
Before Chang Haonan could take action, he turned directly to one of the pages:
“You see, on the section where the fracture occurred, that is, at points 1 and 2, the atomic percentages of the two elements titanium and aluminum are close to each other. At 2:1, and the presence of chromium and niobium is small, indicating that the γ phase, B2 phase and α2 phase all exist, and the ratio is relatively balanced."
"And in the matrix farther away from the crack. In this part, that is, at points 3 and 4, the ratio of titanium and aluminum atoms decreases to 1:1. In addition, the content of chromium and niobium also increases accordingly, indicating that the proportion of α2 phase and B2 components appears at this time. There is a significant increase, while the γ phase decreases accordingly..."
"..."
If we put aside the general situation, and be "surprised" like this and then immediately instill a lot of representation results, the level will be very high or low. Wait for a while before you can hear it.
Fortunately, Chang Haonan was already thinking about this matter in his mind at the moment, and his own ability to read pictures was first-rate, so he could keep up with the other party's thinking.
After Hang Zhibin finished a long paragraph, he directly went to the final conclusion:
"So it can be proved that during the process of crack formation, simultaneous cracking occurs at the cracking position. The eutectoid reaction of α→γ+β!”
“Yes!”
Hang Zhibin nodded quickly:
"It is completely consistent with your previous speculation. As long as the proportion of α2 brittle phase in the alloy can be reduced, the tensile strength inside the material can be increased and the stress generation can be reduced at the same time."
"Our current plan is, Preheating the substrate during the molding process can, on the one hand, suppress the peritectic reaction and reduce the generation of α2 phase, and on the other hand, it can also control the cooling rate to a certain extent.”
Compared to his excitement. , Chang Haonan's reaction was quite dull.
Actually, a few days ago, he had improved the formation of cracks by increasing the temperature of the immersion liquid during the drilling process.
So, this result can be regarded as adding a layer of theoretical insurance at most, and it will not surprise him.
"Substrate preheating is only one aspect. In addition to cracks caused by cooling too quickly, there is another problem during the processing of 4722."
Chang Haonan stood up as he spoke, and took some food from the small table next to him. He picked up the thermos, poured two glasses of water respectively, and then handed one to Hang Zhibin in front:
"You have just conducted EBSD and micromorphology observations, and you should be able to find that during titanium-aluminum alloy forming During the process, because the local temperature of the molten pool will be higher than the evaporation point of aluminum, part of the gas containing aluminum will evaporate and be lost, and those gases that have no time to evaporate will form small holes when they solidify."
"These. A large residual stress will accumulate near the hole. Although the distribution is not as extensive as the stress caused by cooling, it will also induce cracks around it. And because this kind of hot crack does not produce secondary cracks during the expansion process, the development of the main crack On the contrary, it will be more obvious.”
“Am I right?”
"Ah...ah?"
Hang Zhibin had just raised his hand in the air, but when he heard Chang Haonan's analysis, his whole body froze in place as if he had been hit by a thunderbolt.
Because this is exactly what he wants to tell Chang Haonan next.
This is also the most important finding in the report just now.
The result......
The other party knew it in advance without even looking at it?
About half a minute later, Hang Zhibin reacted and quickly took the cup into his hand:
"This...is this also what you guessed?"
You know, This problem is unique to the thermoforming process.
The cold working process cannot reach the melting point of titanium alloy at all, and it is impossible to even observe the phenomenon.
"How is it possible..."
Chang Haonan smiled and waved his hand.
"Oh..."
Hearing that Chang Haonan's explanation was the same as what he had just thought, Hang Zhibin finally breathed a sigh of relief and waited for further explanation.
But before he could take his next breath, Chang Haonan continued:
"I calculated this." "..."
Hang Zhibin held the cup and didn't know how to respond for a while.
I wanted to lower my head and drink water tactically to delay, but I forgot that the water had just been poured from the thermos bottle...
Fortunately, Chang Haonan was standing in front of the window with his back to Looking at him, he didn't notice that the other person almost burned his tongue. He just continued to introduce his conclusion:
"Through molecular dynamics research results, at higher temperatures, the expansion rate of aluminum oxide is much slower than that of titanium oxide with similar thermodynamic stability. As a result, titanium alloys containing aluminum cannot rely on oxidation like aluminum alloys containing titanium. The aluminum film is used to protect itself, and the chromium and niobium in the 4722 alloy are added as anti-oxidation elements.”
“But these two elements exist in the form of solid solution in the base alloy. , thus affecting the generation mode of alumina, which determines that during the process of heating-oxidation-melting, aluminum will be more easily lost in the form of gas..."
"..."
In the middle of listening, Hang Zhibin had already put the cup in his hand aside, took out a pen and paper and started recording——
When he first met Chang Haonan, he once said that he had studied some Computational materials science, that’s not a compliment.
Although I didn’t really study it well at the time, one thing was very certain.
Traditional materials science is based on analyzing the causes of phenomena and then working backwards to summarize the rules and then generate theories.
The research process of computational materials science is the opposite of this.
First there is the theory, then the laws are deduced, and finally the phenomenon is obtained.
In other words, although the current application scope of this discipline is still relatively narrow, as long as the application is successful, it means that the problem has been discovered and a solution to the problem has been found.
Like it is now.
“We will further adjust the forming parameters of laser selective melting to minimize local temperature fluctuations, which may cause aluminum to evaporate.”
Hang Zhibin responded while writing the last word in his notebook A few words.
Then, the pen tip is retracted with a click.
“Adjusting parameters is only a temporary measure.”
Chang Haonan sat back on his chair and said:
"In the long run, as I just said, chromium and niobium are added to improve the oxidation resistance of titanium alloys, but even during the molding process Controlling the temperature to perfection will also cause the aluminum to be concentrated on the upper surface of the final molding, while the content in other parts will decrease, which in turn will have an adverse effect on the oxidation resistance."
"I don't care what the British are going to use. Such a coating can be used to solve this problem, but on the one hand, we are completely missing this part of the data. On the other hand, even if there is a coating, it is not a bad thing to improve the antioxidant capacity of the substrate itself. "
Hang Zhibin thought. After a while:
“So, you want to improve on the British material?”
If there was anyone sitting in front of him except Chang Haonan...and Academician Cao Xiaochun, he would have dropped his pen on the table——
Materials science is not just about changing elements The ingredients or proportions are all.
Now they are not even sure about the process parameters of 4722, and they even need to complete the remaining parts through a lot of experiments.
In this case, just thinking about improving materials is almost equivalent to trying to run a marathon without even learning to crawl.
Totally whimsical.
Not only does it fail to achieve the purpose of improving performance, but it may even fail to achieve the performance that others had before improvements due to insufficient understanding of the original materials.
There is a high probability that what you get is pure waste.
However, considering Chang Haonan's actual situation, Hang Zhibin clicked again and pressed the pen tip out.
“Exactly.”
Chang Haonan knocked on the table with excitement:
"I randomly tried using several rare earth elements, and accidentally discovered that replacing a certain amount of chromium and niobium with trace amounts of ytterbium and cerium can refine the grains, purify the matrix, and improve the adhesion of the oxide film. "
"In addition, due to different solid solution conditions, these two elements, especially ytterbium, can also promote the selective oxidation of Al, thereby reducing the difficulty of local temperature control in industrial production. "
As he spoke, he took out the calculation results that had just been sent a few hours ago and handed them to Hang Zhibin:
"Of course, I am just providing an idea and a specific experiment. You still need to do the above-mentioned things, so this is the next research direction.”
“As for now...in order to restore the British 4722, you still have to work on the process parameters of laser selective melting. I'm in a hurry..."
(End of this chapter)