Study On The Composite Process Of Internal Pressure Forming-in-situ Reaction Synthesis Of NiAl Alloy Thin-walled Components

Hypersonic aircraft urgently needs new lightweight heat-resistant alloys instead of Nibased superalloys to manufacture key components such as inlets to achieve structural weight reduction.NiAl alloys have become one of the preferred materials due to their lower density and better high-temperature performance.Generally,the traditional manufacturing method of light-weight heat-resistant alloy complex thin-walled components is to first prepare the plate by the method of "melting-casting-forging-rolling",and then secondary forming the final component from the plate,that is,"forming material first,then forming".However,due to the inherent brittleness of NiAl alloys,NiAl plates and their complex curved thin-walled components are difficult to prepare by traditional methods.Based on this,this paper proposes a new method for manufacturing NiAl thin-walled components using the "internal pressure bulging-in-situ reaction" composite forming process of Ni/Al laminated foil.The principle is: using Niand Al foil as raw materials,first hot pressing Ni/Al composite plate,and then pressure bulge inside the composite plate to obtain a Ni/Al laminated thin-walled component.Finally,the Ni/Al in the component is reacted at high temperature and high pressure to form a NiAl intermetallic compound.This method uses the reverse thinking of "forming first,then finished material",so that the Ni/Al composite plate is formed first,the NiAl intermetallic compound is formed later,and the NiAl is not formed again after the formation,thus,the direct high temperature forming of brittle NiAl plates and the resulting deterioration of microstructure and properties can be avoidedBy studying the preparation process,microstructure and mechanical properties of Ni/Al composite plates,NiAl alloy plates,NiAl alloy tapered cylindrical shells and NiAl alloy spherical crown thin shells,the uniaxial tension and internal pressure expansion of Ni/Al composite plates are revealed The law of shape deformation reveals the combined forming mechanism of NiAl alloy plate and thin-walled component by internal pressure bulging-in-situ reaction.The main conclusions obtained are as follows:The Ni/Al composite plate was successfully prepared by the hot pressing process of Ni/Al laminated foil.The plasticity of the composite plate increases first and then decreases with the extension of the first-order reaction time,and increases with the increase of temperature.The room temperature elongation rates of the Ni/Al composite plates prepared by the first-order reaction 0h,0.5h,and 2h are 12%,18%,and 0%,respectively,and the elongation rates at 600°C reach 22%,62%,and 48%,respectively,therefore,the reasonable preparation process of Ni/Al composite plate is as follows: 640℃/10MPa/0.5h;The reasonable forming temperature is 600℃.Using Ni/Al laminated foil hot pressing process,NiAl alloy plate was successfully prepared through two stages of primary reaction and secondary reaction.The reasonable firststage reaction process parameter is 640℃/10MPa/4h,and the second-stage reaction process parameter is 1100℃/15MPa/2h.The prepared NiAl alloy plate has a plasticity of 0 at room temperature and a tensile strength of 63 MPa.As the deformation temperature increases,the NiAl alloy sheet softens,showing increased plasticity and decreased strength.The elongation and strength at 800℃,900℃,and 1000℃ can reach 44%,157MPa;69%,96MPa;78%,64 MPa,respectively.The NiAl alloy conical cylindrical shell was successfully prepared by the composite forming process of internal pressure bulging-in-situ reaction of solid particles.The cylindrical shell has a good forming effect without cracks,wrinkles and other macro defects;the cylindrical shell is composed of a single NiAl phase,with thick coarse-grained layers and fine-grained layers alternately arranged,which is a typical bimodal structure with tight interlayer bonding and no holes,etc.defect.The hardness distribution of the NiAl alloy cone shell is uniform,about 350HV;the tensile strength at 1000℃ is 71 MPa,and the elongation is 74%.The existence of foil joints during the reaction preparation process will reduce the mechanical properties of the components.The thin shell of NiAl alloy spherical crown was successfully prepared by gas internal pressure bulging-in-situ reaction composite forming process.The Ni/Al composite plate prepared under the 640℃/10MPa/0.5h hot pressing process has the best bulging performance at 600℃,the bulging height can reach 22.03 mm,and the limit bulging rate is 36%.The wall thickness from the bottom to the top of the bulging spherical shell gradually decreases,and the phase layer interface changes from flat to high and low undulations,and the degree of undulation increases with the increase of deformation,which should be the result of the coordination of the heterogeneous phase layer deformation.A thin NiAl alloy spherical crown shell was successfully prepared using a spherical crown mold cavity with a height of 20 mm.The atomic percentage contents of the original Nilayer and Al layer at the apex of the bulging spherical shell were 52.38Ni-47.62 Al and 49.81%Ni-50.19%Al,respectively.The Ni/Al atomic content ratio is slightly deviated,but it is already in the category of NiAl alloy composition.