Is there a significant difference in the performance of metal 3D printed parts before and after heat treatment?

1. Microstructure: a change in quality from flaws to density
The metal 3D printing process involves quickly heating and cooling the material, which causes a lot of tiny flaws to occur inside the objects. For instance, in the laser powder bed melting (LPBF) method, the melt pool cools down quickly, which makes coarse columnar crystals with high-density dislocations and micropores at the grain boundaries. These flaws not only lower the density of the material (typically 98%–99.5%), but they also cause cracks to form, which makes the parts more weaker in terms of their mechanical qualities.
Heat treatment improves microstructure by doing the following:
Densification: Hot isostatic pressing (HIP) treatment works with high temperature (typically 0.7-0.9 times the melting point of the material) and high pressure (100-200MPa) to shut the part's internal pores and microcracks. For instance, after HIP treatment, the density of high-temperature alloy parts for a certain aviation engine went from 99.2% to 99.99%, and the parts could last five times longer before breaking down.
Refining the grain: The process of recrystallization during annealing can make the grain size smaller. For instance, annealing aluminum alloy printed parts at 350 °C for 2 hours reduces the grain size from 100 μm to 20 μm and increases the yield strength by 15%.
Control of phase change: When you quench and temper steel, you can make a dual-phase structure comprising martensite and residual austenite. For instance, after being quenched at 1050 °C and tempered at 200 °C, the hardness of mold steel printed parts reaches 58HRC, and they are three times more resistant to wear than untreated parts.
2, Mechanical properties: going from being fragile to being strong
Heat treatment is very important for making the mechanical properties of metal 3D printed items better. For example, when looking at the high-temperature alloy GH4169, the printed parts have a little lower tensile strength and yield strength than the forged parts, but the elongation at break and cross-sectional shrinkage are much worse. After routine heat treatment (stress relief annealing and homogenization annealing), its tensile qualities at room temperature and high temperatures meet or surpass the norms for forging. Its high-temperature durability is also superior than that of forged parts.
The disparities in performance are shown in:
Strength enhancement: The quenching procedure makes a martensitic structure by cooling it down quickly, which makes it much harder. For instance, after quenching, the tensile strength of printed parts made of nickel-based high-temperature alloy goes up from 460MPa to 585MPa.
Better toughness: Tempering can get rid of quenching stress and make things tougher. For instance, after quenching and tempering at 550 °C, the impact toughness of a printed section of a car transmission shaft went up from 15J/cm² to 35J/cm².
Optimizing fatigue performance: Heat treatment can fix problems inside the material and slow down the spread of fatigue cracks. After heat treatment, the fatigue life of GH4169 printed parts at 650 °C is 20% longer than that of forged parts.
3. Dimensional stability: from bending to exact assurance
Metal 3D printed parts may change size after printing because of residual stress release or changes in the microstructure. This might make it harder to put them together correctly. Heat treatment can greatly improve dimensional stability by making the microstructure more stable and getting rid of stress.
Less deformation: Annealing can make the difference in thermal expansion coefficient between parts less and make machining deformation less. For instance, the diameter deviation of a printed section of a complex flow channel heat exchanger went from ± 0.15mm to ± 0.05mm after annealing.
Long-term stability: Aging treatment can get rid of supersaturated solid solutions in materials and keep their size from changing too much over time. For instance, after being aged at 170 °C for 8 hours, the size change rate of printed aluminum alloy parts dropped from 0.3% per year to 0.05% per year.
Adaptation of complicated structures: Heat treatment can help prevent stress accumulation during processing for complex structures like thin-walled and porous ones. After twofold annealing (700 °C × 2h + 500 °C × 4h), the fatigue limit of titanium alloy orthopedic implants rose from 450 MPa to 600 MPa, which is enough to support the body's weight over time.
4. Special Performance Requirements: Universal to Customized Breakthrough: Heat treatment can also provide metal 3D printed objects unique qualities, which makes them useful in more situations.
Improved resistance to corrosion: Solid solution treatment can dissolve the second phase in the material, which makes it less likely to corrode through electrochemical means. For instance, after being treated with a solution at 1050 °C, the pitting potential of 316L stainless steel printed components went up from 320mV to 450mV, which is good for use in maritime conditions.
Control of magnetic properties: Heat treatment can change the grain orientation and residual stress of soft magnetic materials to make their magnetic characteristics better. For instance, after being heated to 750 °C, the magnetic permeability of a given part of a solenoid valve goes up by 20% and the amount of energy used goes down by 15%.
Improving biocompatibility: Medical implants need to be heated to get rid of surface contaminants and make a passivation film. For instance, the surface roughness Ra of titanium alloy orthopedic implants went from 3.2 μ m to 0.8 μ m following acid washing and annealing at 500 °C, and the rate at which cells stuck to the implants went up by 40%.
5. A case study: Heat treatment can make CuCrZr alloy characteristics much better in a way that is not expected.
Because it has great conductivity and mechanical qualities, CuCrZr alloy is often utilized in parts of airplane engines. However, it is hard and expensive to make complicated structures using typical processing methods. The CuCrZr alloy made with SLM technique is quite strong (yield strength 411MPa) but not very good at conducting electricity (31% IACS). After being heated to 500 °C for an hour, its tensile strength went up to 585 MPa and its conductivity went up to 64% IACS. This is similar to how well typical treated alloys work. This scenario shows that heat treatment is an important step in getting the most out of metal 3D printing materials.